Merge origin/dev (Feature 03) into Feature 04 integration

Feature 03 made the OIDC variables required, so the Feature 04 boot tests'
loadConfig helper now sets them alongside the secret key file.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -30,14 +30,32 @@ export MEALQUEST_PUBLIC_URL=http://localhost:5173
 export MEALQUEST_DATA_DIR="$HOME/.mealquest-dev"
 export MEALQUEST_SHUTDOWN_TIMEOUT=10s
 export MEALQUEST_SECRET_KEY_FILE="$HOME/.mealquest-dev/secret_key"
+# Authentik OAuth2/OpenID provider for MealQuest (redirect URI:
+# $MEALQUEST_PUBLIC_URL/auth/callback). Save its client secret to the file.
+export MEALQUEST_OIDC_ISSUER=https://auth.example.com/application/o/mealquest/
+export MEALQUEST_OIDC_CLIENT_ID=mealquest
+export MEALQUEST_OIDC_CLIENT_SECRET_FILE="$HOME/.mealquest-dev/oidc_client_secret"
+export MEALQUEST_OIDC_ALLOWED_GROUPS=mealquest-admin
+# Optional: sessions end after MEALQUEST_SESSION_IDLE unused (default 720h)
+# and always MEALQUEST_SESSION_MAX after sign-in (default 4320h).
+# export MEALQUEST_SESSION_IDLE=720h
+# export MEALQUEST_SESSION_MAX=4320h
+# Optional: comma-separated IPs/CIDRs of reverse proxies whose
+# X-Forwarded-For/-Proto headers are honoured (production: Traefik). Unset
+# trusts no peer, which is right for local development.
+# export MEALQUEST_TRUSTED_PROXY=10.60.1.33
 make dev
 ```
 
 `make dev` runs the Go server on `:8080` and the Vite dev server on `:5173`
 (which proxies `/api`, `/auth` and `/media` to `:8080`). Open
 http://localhost:5173. Configuration is environment-only and fails fast:
-every variable above is required, and secrets are read only from files named
-by `*_FILE` variables.
+every variable above is required except the commented-out session
+lifetimes (when set they must be positive, with MAX at least IDLE) and
+trusted proxy list (every entry must be an IP or CIDR), and
+secrets are read only from files named by `*_FILE` variables. `MEALQUEST_PUBLIC_URL`, `MEALQUEST_OIDC_ISSUER` and the
+endpoints the issuer advertises must be `https://`; plain `http://` is
+accepted only for `localhost`, `127.0.0.1` and `[::1]`.
 
 ## Common commands
 

cmd/server/boot_test.go

@@ -34,15 +34,24 @@ func useBootMigrations(t *testing.T, m fstest.MapFS) {
 // holds keyFile. Tests that call it must not run in parallel.
 func loadConfig(t *testing.T, keyFile string) config.Config {
 	t.Helper()
-	keyPath := filepath.Join(t.TempDir(), "secret_key")
+	dir := t.TempDir()
+	keyPath := filepath.Join(dir, "secret_key")
 	if err := os.WriteFile(keyPath, []byte(keyFile), 0o600); err != nil {
 		t.Fatal(err)
 	}
+	clientSecretPath := filepath.Join(dir, "oidc_client_secret")
+	if err := os.WriteFile(clientSecretPath, []byte("client-secret\n"), 0o600); err != nil {
+		t.Fatal(err)
+	}
 	t.Setenv(config.EnvHTTPAddr, "127.0.0.1:0")
 	t.Setenv(config.EnvPublicURL, "http://localhost")
 	t.Setenv(config.EnvDataDir, t.TempDir())
 	t.Setenv(config.EnvShutdownTimeout, "1s")
 	t.Setenv(config.EnvSecretKeyFile, keyPath)
+	t.Setenv(config.EnvOIDCIssuer, "https://auth.example.com/application/o/mealquest/")
+	t.Setenv(config.EnvOIDCClientID, "mealquest")
+	t.Setenv(config.EnvOIDCClientSecretFile, clientSecretPath)
+	t.Setenv(config.EnvOIDCAllowedGroups, "mealquest-admin")
 	cfg, err := config.Load()
 	if err != nil {
 		t.Fatal(err)

cmd/server/main.go

@@ -13,7 +13,9 @@ import (
 	"syscall"
 	"time"
 
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/auth"
 	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/config"
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/forwarded"
 	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/frontend"
 	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/secretbox"
 	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/server"
@@ -31,7 +33,7 @@ func main() {
 		os.Exit(1)
 	}
 
-	logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
+	logger := slog.New(forwarded.LogHandler(slog.NewJSONHandler(os.Stdout, nil)))
 	if err := run(cfg, logger); err != nil {
 		logger.Error("server stopped", "error", err)
 		os.Exit(1)
@@ -56,7 +58,23 @@ func run(cfg config.Config, logger *slog.Logger) error {
 		}
 	}()
 
-	router, err := server.NewRouter(logger, version, frontend.Assets())
+	sessions, err := auth.NewSessionManager(db, cfg.SessionIdle, cfg.SessionMax)
+	if err != nil {
+		return err
+	}
+	authFlow, err := auth.New(ctx, auth.Config{
+		Issuer:        cfg.OIDCIssuer.String(),
+		ClientID:      cfg.OIDCClientID,
+		ClientSecret:  cfg.OIDCClientSecret.Reveal(),
+		PublicURL:     cfg.PublicURL,
+		SecretKey:     []byte(cfg.SecretKey.Reveal()),
+		AllowedGroups: cfg.OIDCAllowedGroups,
+	}, sessions, logger)
+	if err != nil {
+		return err
+	}
+
+	router, err := server.NewRouter(logger, version, cfg.TrustedProxy, authFlow, sessions, frontend.Assets())
 	if err != nil {
 		return err
 	}
@@ -124,6 +142,7 @@ func logListening(logger *slog.Logger, cfg config.Config) {
 	logger.Info("listening",
 		"addr", cfg.HTTPAddr,
 		"public_origin", cfg.PublicOrigin(),
+		"trusted_proxy", cfg.TrustedProxy,
 		"data_dir", cfg.DataDir,
 		"version", version,
 	)

docs/ARCHITECTURE.md

@@ -29,6 +29,15 @@ docker compose project "mealquest" — 10.60.1.14
 One Go service serves the API, the auth flow, media and the PWA. Its SQLite
 database is replicated by Litestream to the NAS.
 
+Traefik terminates TLS. The service honours `X-Forwarded-For` and
+`X-Forwarded-Proto` only from peers listed in `MEALQUEST_TRUSTED_PROXY`
+(comma-separated IPs/CIDRs; production lists `10.60.1.33`); from any other
+peer they are ignored. The client is the rightmost `X-Forwarded-For` address
+that is not a trusted proxy. The resolved client IP is added as `client_ip`
+to every log line written while handling a request. The OIDC redirect URI
+and the Secure cookies are fixed by `MEALQUEST_PUBLIC_URL`, never by request
+headers, so sign-in works whichever peer the request arrives from.
+
 ## Repository layout
 
 | Path | Purpose |

go.mod

@@ -3,13 +3,16 @@ module code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest
 go 1.25.0
 
 require (
+	github.com/coreos/go-oidc/v3 v3.21.0
 	github.com/go-chi/chi/v5 v5.3.1
 	github.com/oklog/ulid/v2 v2.1.2
+	golang.org/x/oauth2 v0.36.0
 	modernc.org/sqlite v1.59.0
 )
 
 require (
 	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/go-jose/go-jose/v4 v4.1.4 // indirect
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/mattn/go-isatty v0.0.24 // indirect
 	github.com/ncruces/go-strftime v1.0.0 // indirect

go.sum

@@ -1,7 +1,11 @@
+github.com/coreos/go-oidc/v3 v3.21.0 h1:wZo4Q9Pum8dYEj0eMUPrqR+kvuGkeUplbLpNCkBqoWM=
+github.com/coreos/go-oidc/v3 v3.21.0/go.mod h1:DYCf24+ncYi+XkIH97GY1+dqoRlbaSI26KVTCI9SrY4=
 github.com/dustin/go-humanize v1.0.1 h1:GzkhY7T5VNhEkwH0PVJgjz+fX1rhBrR7pRT3mDkpeCY=
 github.com/dustin/go-humanize v1.0.1/go.mod h1:Mu1zIs6XwVuF/gI1OepvI0qD18qycQx+mFykh5fBlto=
 github.com/go-chi/chi/v5 v5.3.1 h1:3j4HZLGZQ3JpMCrPJF/Jl3mYJfWLKBfNJ6quurUGCf8=
 github.com/go-chi/chi/v5 v5.3.1/go.mod h1:R+tYY2hNuVUUjxoPtqUdgBqevM9s9njzkTLutVsOCto=
+github.com/go-jose/go-jose/v4 v4.1.4 h1:moDMcTHmvE6Groj34emNPLs/qtYXRVcd6S7NHbHz3kA=
+github.com/go-jose/go-jose/v4 v4.1.4/go.mod h1:x4oUasVrzR7071A4TnHLGSPpNOm2a21K9Kf04k1rs08=
 github.com/google/pprof v0.0.0-20260802141513-ef3492d7dac3 h1:LMLX+LgTNWpfvCBdFebv6EsYotImrt/Ppc5cXIriCSo=
 github.com/google/pprof v0.0.0-20260802141513-ef3492d7dac3/go.mod h1:jl5iWTm0/hd5PjEYEOuwAJ57L/CibdZfrqZ5XA5GrCk=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
@@ -19,6 +23,8 @@ github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec h1:W09IVJc94
 github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec/go.mod h1:qqbHyh8v60DhA7CoWK5oRCqLrMHRGoxYCSS9EjAz6Eo=
 golang.org/x/mod v0.38.0 h1:MECBjubtXD7yj4HrhIUcywNaGeNVUdfVnxmPajOk4yk=
 golang.org/x/mod v0.38.0/go.mod h1:V6Xz0pq8TQ3dGqVQ1FVHuelZpAL0uNhSkk9ogYP3c40=
+golang.org/x/oauth2 v0.36.0 h1:peZ/1z27fi9hUOFCAZaHyrpWG5lwe0RJEEEeH0ThlIs=
+golang.org/x/oauth2 v0.36.0/go.mod h1:YDBUJMTkDnJS+A4BP4eZBjCqtokkg1hODuPjwiGPO7Q=
 golang.org/x/sync v0.22.0 h1:SZjpbeLmrCk4xhRSZFNZW5gFUeCeFgjekvI/+gfScek=
 golang.org/x/sync v0.22.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
 golang.org/x/sys v0.47.0 h1:o7XGOvZQCADBQQ4Y7VNq2dRWQR7JmOUW8Kxx4ZsNgWs=

internal/auth/actor.go

@@ -0,0 +1,45 @@
+package auth
+
+import (
+	"context"
+	"slices"
+)
+
+// Actor is the signed-in household member a request acts for. Handlers
+// record Actor.Subject as updated_by on edits.
+type Actor struct {
+	Subject string
+	Email   string
+	Name    string
+	Groups  []string
+}
+
+// Actor returns the household member s belongs to.
+func (s Session) Actor() Actor {
+	return Actor{Subject: s.Subject, Email: s.Email, Name: s.Name, Groups: slices.Clone(s.Groups)}
+}
+
+type sessionKey struct{}
+
+// WithSession returns a copy of ctx carrying s. The session middleware calls
+// it for every authenticated request.
+func WithSession(ctx context.Context, s Session) context.Context {
+	return context.WithValue(ctx, sessionKey{}, s)
+}
+
+// SessionFrom returns the session WithSession stored in ctx. ok is false when
+// ctx has none, which behind the session middleware means a wiring bug.
+func SessionFrom(ctx context.Context) (s Session, ok bool) {
+	s, ok = ctx.Value(sessionKey{}).(Session)
+	return s, ok
+}
+
+// ActorFrom returns the actor of the session WithSession stored in ctx. ok is
+// false when ctx has none.
+func ActorFrom(ctx context.Context) (actor Actor, ok bool) {
+	s, ok := SessionFrom(ctx)
+	if !ok {
+		return Actor{}, false
+	}
+	return s.Actor(), true
+}

internal/auth/actor_test.go

@@ -0,0 +1,40 @@
+package auth
+
+import (
+	"context"
+	"slices"
+	"testing"
+)
+
+func TestActorContext(t *testing.T) {
+	t.Parallel()
+	if _, ok := ActorFrom(context.Background()); ok {
+		t.Error("ActorFrom found an actor in an empty context")
+	}
+	if _, ok := SessionFrom(context.Background()); ok {
+		t.Error("SessionFrom found a session in an empty context")
+	}
+	s := Session{Subject: "user-123", Email: "cook@example.com", Name: "Home Cook", Groups: []string{"mealquest-admin"}, CSRFToken: "t"}
+	ctx := WithSession(context.Background(), s)
+	gotSession, ok := SessionFrom(ctx)
+	if !ok || gotSession.Subject != s.Subject || gotSession.CSRFToken != s.CSRFToken {
+		t.Errorf("SessionFrom = %+v (ok=%v), want %+v", gotSession, ok, s)
+	}
+	got, ok := ActorFrom(ctx)
+	if !ok || got.Subject != s.Subject || got.Email != s.Email || got.Name != s.Name || !slices.Equal(got.Groups, s.Groups) {
+		t.Errorf("ActorFrom = %+v (ok=%v), want the session's actor", got, ok)
+	}
+}
+
+func TestSessionActor(t *testing.T) {
+	t.Parallel()
+	s := Session{Subject: "user-123", Email: "cook@example.com", Name: "Home Cook", Groups: []string{"mealquest-admin"}, CSRFToken: "t"}
+	a := s.Actor()
+	if a.Subject != s.Subject || a.Email != s.Email || a.Name != s.Name || !slices.Equal(a.Groups, s.Groups) {
+		t.Errorf("Actor = %+v, want the session's identity", a)
+	}
+	a.Groups[0] = "changed"
+	if s.Groups[0] != "mealquest-admin" {
+		t.Error("Actor shares the session's groups slice")
+	}
+}

internal/auth/auth.go

@@ -0,0 +1,439 @@
+// Package auth signs the household in with Authentik over OpenID Connect.
+// The service is a confidential client: the authorization code, tokens and
+// client secret stay on the server and never reach JavaScript.
+package auth
+
+import (
+	"context"
+	"crypto/rand"
+	"crypto/subtle"
+	"errors"
+	"fmt"
+	"log/slog"
+	"net/http"
+	"net/url"
+	"slices"
+	"sync/atomic"
+	"time"
+
+	"github.com/coreos/go-oidc/v3/oidc"
+	"github.com/go-chi/chi/v5"
+	"golang.org/x/oauth2"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/secureurl"
+)
+
+// Routes owned by this package.
+const (
+	LoginPath    = "/auth/login"
+	CallbackPath = "/auth/callback"
+	LogoutPath   = "/auth/logout"
+)
+
+// providerTimeout bounds every request to the identity provider.
+const providerTimeout = 10 * time.Second
+
+// scopes requested at login.
+var scopes = []string{oidc.ScopeOpenID, "profile", "email", "groups", oidc.ScopeOfflineAccess}
+
+// Claims are the verified ID token claims handed to the session layer.
+type Claims struct {
+	Subject           string   `json:"sub"`
+	Email             string   `json:"email"`
+	EmailVerified     bool     `json:"email_verified"`
+	Name              string   `json:"name"`
+	PreferredUsername string   `json:"preferred_username"`
+	Groups            []string `json:"groups"`
+}
+
+// Sessions is the session layer. StartSession is called once per successful
+// login with claims from a verified ID token; it must set the session cookie
+// on w. EndSession is called on logout; it must end the session r carries,
+// if any, and clear the cookie on w. A returned error fails the request with
+// 500.
+type Sessions interface {
+	StartSession(w http.ResponseWriter, r *http.Request, claims Claims) error
+	EndSession(w http.ResponseWriter, r *http.Request) error
+}
+
+// Config is what New needs to reach the identity provider.
+type Config struct {
+	// Issuer is the exact issuer URL; discovery runs against it.
+	Issuer       string
+	ClientID     string
+	ClientSecret string
+	// PublicURL is the service's public URL; its origin prefixes CallbackPath
+	// to form the redirect URI.
+	PublicURL *url.URL
+	// SecretKey is the server key the login cookie's signing key derives from.
+	SecretKey []byte
+	// AllowedGroups are the household's groups; a sign-in is refused unless
+	// the account is in at least one of them.
+	AllowedGroups []string
+}
+
+// Auth serves the login and callback routes.
+type Auth struct {
+	oauth    oauth2.Config
+	verifier *oidc.IDTokenVerifier
+	provider *oidc.Provider
+	client   *http.Client
+	cookie   loginCookie
+	sessions Sessions
+	allowed  []string
+	// endSessionURL is the provider's end_session_endpoint; logout ends
+	// there so the provider's own session ends too.
+	endSessionURL string
+	logger        *slog.Logger
+}
+
+// New discovers the provider at cfg.Issuer and returns the login flow. It
+// fails if discovery fails or the issuer the provider reports differs.
+func New(ctx context.Context, cfg Config, sessions Sessions, logger *slog.Logger) (*Auth, error) {
+	switch {
+	case cfg.Issuer == "", cfg.ClientID == "", cfg.ClientSecret == "":
+		return nil, errors.New("auth: issuer, client ID and client secret are required")
+	case cfg.PublicURL == nil:
+		return nil, errors.New("auth: public URL is required")
+	case len(cfg.SecretKey) == 0:
+		return nil, errors.New("auth: secret key is required")
+	case sessions == nil:
+		return nil, errors.New("auth: session layer is required")
+	case len(cfg.AllowedGroups) == 0:
+		return nil, errors.New("auth: at least one allowed group is required")
+	}
+
+	if err := checkEndpoint("issuer", cfg.Issuer); err != nil {
+		return nil, err
+	}
+
+	client := &http.Client{Timeout: providerTimeout, CheckRedirect: checkRedirect}
+	discovery := *client
+	recorder := &statusRecorder{next: http.DefaultTransport}
+	discovery.Transport = recorder
+	provider, err := oidc.NewProvider(oidc.ClientContext(ctx, &discovery), cfg.Issuer)
+	if err != nil {
+		return nil, discoveryError(err, int(recorder.status.Load()))
+	}
+	endpoint := provider.Endpoint()
+	var discovered struct {
+		JWKSURI       string `json:"jwks_uri"`
+		EndSessionURI string `json:"end_session_endpoint"`
+	}
+	if err := provider.Claims(&discovered); err != nil {
+		return nil, fmt.Errorf("auth: OIDC discovery: %w", err)
+	}
+	// The token endpoint receives the client secret and the key set decides
+	// which tokens verify, so every endpoint used must pass the same rule.
+	for _, e := range []struct{ name, raw string }{
+		{"authorization endpoint", endpoint.AuthURL},
+		{"token endpoint", endpoint.TokenURL},
+		{"JWKS endpoint", discovered.JWKSURI},
+		{"end session endpoint", discovered.EndSessionURI},
+		// Groups come from userinfo when the ID token carries none, and the
+		// access token is sent there.
+		{"userinfo endpoint", provider.UserInfoEndpoint()},
+	} {
+		if err := checkEndpoint(e.name, e.raw); err != nil {
+			return nil, err
+		}
+	}
+	// client_secret_basic, the OIDC default; no auto-detection retries.
+	endpoint.AuthStyle = oauth2.AuthStyleInHeader
+
+	return &Auth{
+		oauth: oauth2.Config{
+			ClientID:     cfg.ClientID,
+			ClientSecret: cfg.ClientSecret,
+			Endpoint:     endpoint,
+			RedirectURL:  cfg.PublicURL.Scheme + "://" + cfg.PublicURL.Host + CallbackPath,
+			Scopes:       scopes,
+		},
+		verifier: provider.Verifier(&oidc.Config{
+			ClientID:             cfg.ClientID,
+			SupportedSigningAlgs: []string{oidc.RS256},
+		}),
+		provider:      provider,
+		client:        client,
+		allowed:       slices.Clone(cfg.AllowedGroups),
+		cookie:        newLoginCookie(cfg.SecretKey),
+		sessions:      sessions,
+		endSessionURL: discovered.EndSessionURI,
+		logger:        logger,
+	}, nil
+}
+
+// statusRecorder records the status of the last response it carries.
+type statusRecorder struct {
+	next   http.RoundTripper
+	status atomic.Int32
+}
+
+func (s *statusRecorder) RoundTrip(req *http.Request) (*http.Response, error) {
+	resp, err := s.next.RoundTrip(req)
+	if err == nil {
+		s.status.Store(int32(resp.StatusCode))
+	}
+	return resp, err
+}
+
+// discoveryError reports a failed discovery. go-oidc puts the provider's
+// response body in its error for a non-200 discovery response, so that
+// error is replaced by the status alone. Transport errors carry no response
+// content and keep their cause.
+func discoveryError(err error, status int) error {
+	var urlErr *url.Error
+	if !errors.As(err, &urlErr) && status != 0 && status != http.StatusOK {
+		return fmt.Errorf("auth: OIDC discovery: provider answered HTTP %d", status)
+	}
+	return fmt.Errorf("auth: OIDC discovery: %w", err)
+}
+
+// checkEndpoint applies secureurl.Check to the provider URL raw, naming the
+// endpoint in the error.
+func checkEndpoint(name, raw string) error {
+	u, err := url.Parse(raw)
+	if err != nil {
+		return fmt.Errorf("auth: OIDC %s %q is not a valid URL", name, raw)
+	}
+	if err := secureurl.Check(u); err != nil {
+		return fmt.Errorf("auth: OIDC %s %q: %w", name, raw, err)
+	}
+	return nil
+}
+
+// maxRedirects matches net/http's default redirect limit.
+const maxRedirects = 10
+
+// checkRedirect is the provider client's redirect policy. On a 307 or 308 to
+// the same host Go resends the body and Authorization header, which carry the
+// code and client secret, so every target must pass secureurl.Check and an
+// https:// request never follows a redirect to plain http://, even loopback.
+func checkRedirect(req *http.Request, via []*http.Request) error {
+	if len(via) >= maxRedirects {
+		return fmt.Errorf("stopped after %d redirects", maxRedirects)
+	}
+	if err := secureurl.Check(req.URL); err != nil {
+		return fmt.Errorf("redirect refused: %w", err)
+	}
+	if via[len(via)-1].URL.Scheme == "https" && req.URL.Scheme != "https" {
+		return errors.New("redirect refused: https:// to plain http:// downgrade")
+	}
+	return nil
+}
+
+// Mount registers GET LoginPath, GET CallbackPath and POST LogoutPath on r.
+func (a *Auth) Mount(r chi.Router) {
+	r.Get(LoginPath, a.login)
+	r.Get(CallbackPath, a.callback)
+	r.Post(LogoutPath, a.logout)
+}
+
+// EndSessionURL is the provider's end_session_endpoint.
+func (a *Auth) EndSessionURL() string { return a.endSessionURL }
+
+// login starts the authorization code flow with PKCE (S256). The optional
+// "return" query parameter must be a same-origin path; anything else fails
+// the login with 400.
+func (a *Auth) login(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Cache-Control", "no-store")
+
+	returnTo, err := returnPath(r.URL.Query().Get("return"))
+	if err != nil {
+		http.Error(w, "invalid return path", http.StatusBadRequest)
+		return
+	}
+	state := loginState{
+		State:    rand.Text(),
+		Nonce:    rand.Text(),
+		Verifier: oauth2.GenerateVerifier(),
+		Return:   returnTo,
+	}
+	if err := a.cookie.set(w, state, time.Now()); err != nil {
+		a.logger.ErrorContext(r.Context(), "set login cookie", "error", err)
+		http.Error(w, "internal error", http.StatusInternalServerError)
+		return
+	}
+	http.Redirect(w, r, a.oauth.AuthCodeURL(state.State,
+		oidc.Nonce(state.Nonce),
+		oauth2.S256ChallengeOption(state.Verifier),
+	), http.StatusFound)
+}
+
+// callback completes the flow: it checks state against the login cookie,
+// exchanges the code, verifies the ID token and nonce, then starts a session
+// if the account is in an allowed group. Membership is checked on every
+// login, so an account removed from the group is refused at its next one.
+func (a *Auth) callback(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Cache-Control", "no-store")
+	ctx := r.Context()
+	// The login cookie is single-use.
+	a.cookie.clear(w)
+
+	state, err := a.cookie.read(r, time.Now())
+	if err != nil {
+		a.logger.WarnContext(ctx, "login callback without a valid login cookie", "error", err)
+		http.Error(w, "sign-in expired; start again", http.StatusBadRequest)
+		return
+	}
+	q := r.URL.Query()
+	if subtle.ConstantTimeCompare([]byte(q.Get("state")), []byte(state.State)) != 1 {
+		a.logger.WarnContext(ctx, "login callback state mismatch")
+		http.Error(w, "sign-in state mismatch; start again", http.StatusBadRequest)
+		return
+	}
+	if q.Get("error") != "" {
+		// error and error_description are provider-supplied text; only the
+		// fixed category is logged.
+		a.logger.WarnContext(ctx, "identity provider returned an authorization error")
+		http.Error(w, "sign-in was refused", http.StatusUnauthorized)
+		return
+	}
+	code := q.Get("code")
+	if code == "" {
+		http.Error(w, "missing authorization code", http.StatusBadRequest)
+		return
+	}
+
+	claims, err := a.verify(ctx, code, state)
+	if err != nil {
+		a.logger.WarnContext(ctx, "sign-in failed", "error", err)
+		http.Error(w, "sign-in failed", http.StatusUnauthorized)
+		return
+	}
+	if !a.member(claims.Groups) {
+		if claims.Groups == nil {
+			a.logger.WarnContext(ctx, "sign-in refused: no groups claim in the ID token or userinfo", "subject", claims.Subject)
+		} else {
+			a.logger.WarnContext(ctx, "sign-in refused: not in an allowed group", "subject", claims.Subject)
+		}
+		// A session this browser already holds ends too, so a refused
+		// sign-in never leaves it signed in.
+		if err := a.sessions.EndSession(w, r); err != nil {
+			a.logger.ErrorContext(ctx, "end session", "error", err)
+			http.Error(w, "internal error", http.StatusInternalServerError)
+			return
+		}
+		a.refuse(w, r)
+		return
+	}
+	if err := a.sessions.StartSession(w, r, claims); err != nil {
+		a.logger.ErrorContext(ctx, "start session", "error", err)
+		http.Error(w, "internal error", http.StatusInternalServerError)
+		return
+	}
+	http.Redirect(w, r, state.Return, http.StatusSeeOther)
+}
+
+// logout ends the session, clears the cookie and sends the browser to the
+// provider's end_session_endpoint to end the provider session as well.
+func (a *Auth) logout(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Cache-Control", "no-store")
+	if err := a.sessions.EndSession(w, r); err != nil {
+		a.logger.ErrorContext(r.Context(), "end session", "error", err)
+		http.Error(w, "internal error", http.StatusInternalServerError)
+		return
+	}
+	http.Redirect(w, r, a.endSessionURL, http.StatusSeeOther)
+}
+
+// verify exchanges code for tokens and returns the verified ID token claims.
+// The verifier enforces RS256, issuer, audience and expiry; nonce is checked
+// here. When the ID token has no groups claim, Groups comes from userinfo;
+// it stays nil when neither has one.
+func (a *Auth) verify(ctx context.Context, code string, state loginState) (Claims, error) {
+	token, err := a.oauth.Exchange(context.WithValue(ctx, oauth2.HTTPClient, a.client), code,
+		oauth2.VerifierOption(state.Verifier))
+	if err != nil {
+		return Claims{}, exchangeError(err)
+	}
+	raw, ok := token.Extra("id_token").(string)
+	if !ok || raw == "" {
+		return Claims{}, errors.New("token response has no id_token")
+	}
+	idToken, err := a.verifier.Verify(ctx, raw)
+	if err != nil {
+		return Claims{}, verifyError(err)
+	}
+	if subtle.ConstantTimeCompare([]byte(idToken.Nonce), []byte(state.Nonce)) != 1 {
+		return Claims{}, errors.New("ID token nonce mismatch")
+	}
+	var claims Claims
+	if err := idToken.Claims(&claims); err != nil {
+		return Claims{}, fmt.Errorf("decode ID token claims: %w", err)
+	}
+	if claims.Subject == "" {
+		return Claims{}, errors.New("ID token has no subject")
+	}
+	if claims.Groups == nil {
+		groups, err := a.userinfoGroups(ctx, token, claims.Subject)
+		if err != nil {
+			return Claims{}, err
+		}
+		claims.Groups = groups
+	}
+	return claims, nil
+}
+
+// userinfoGroups returns the groups claim from the userinfo endpoint, nil if
+// it has none. The userinfo subject must match the ID token's subject.
+func (a *Auth) userinfoGroups(ctx context.Context, token *oauth2.Token, subject string) ([]string, error) {
+	info, err := a.provider.UserInfo(oidc.ClientContext(ctx, a.client), oauth2.StaticTokenSource(token))
+	if err != nil {
+		return nil, userinfoError(err)
+	}
+	if info.Subject != subject {
+		return nil, errors.New("userinfo subject does not match the ID token")
+	}
+	var claims struct {
+		Groups []string `json:"groups"`
+	}
+	if err := info.Claims(&claims); err != nil {
+		return nil, fmt.Errorf("decode userinfo claims: %w", err)
+	}
+	return claims.Groups, nil
+}
+
+// userinfoError reduces a failed userinfo request to a fixed category, like
+// exchangeError: go-oidc's error text can carry the response body.
+func userinfoError(err error) error {
+	var transport *url.Error
+	if errors.As(err, &transport) {
+		return fmt.Errorf("userinfo: request failed: %s: %w", transport.Op, transport.Err)
+	}
+	return errors.New("userinfo: endpoint returned an unusable response")
+}
+
+// verifyError reduces a failed ID token verification to a fixed category.
+// go-oidc's error text can carry the JWKS endpoint's response body or
+// token-supplied values, so only the expiry of an expired token is kept.
+func verifyError(err error) error {
+	var expired *oidc.TokenExpiredError
+	if errors.As(err, &expired) {
+		return fmt.Errorf("verify ID token: token expired at %s", expired.Expiry.UTC().Format(time.RFC3339))
+	}
+	return errors.New("verify ID token: token or provider key set rejected")
+}
+
+// member reports whether groups contains an allowed group.
+func (a *Auth) member(groups []string) bool {
+	return slices.ContainsFunc(groups, func(g string) bool { return slices.Contains(a.allowed, g) })
+}
+
+// exchangeError reduces a failed code exchange to a fixed category and safe
+// metadata. The oauth2 error text can carry the token endpoint's response
+// body or error_description, which may echo credentials, so it is dropped.
+func exchangeError(err error) error {
+	var retrieve *oauth2.RetrieveError
+	var transport *url.Error
+	switch {
+	case errors.As(err, &retrieve):
+		return fmt.Errorf("exchange code: token endpoint rejected the request (HTTP %d)", retrieve.Response.StatusCode)
+	case errors.As(err, &transport):
+		// Request failures never carry the response. The URL is dropped: after
+		// a refused redirect it is the provider-supplied Location.
+		return fmt.Errorf("exchange code: token request failed: %s: %w", transport.Op, transport.Err)
+	default:
+		return errors.New("exchange code: token endpoint returned an unusable response")
+	}
+}

internal/auth/cookie.go

@@ -0,0 +1,124 @@
+package auth
+
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+)
+
+const (
+	loginCookieName = "__Host-mealquest_login"
+	loginCookieTTL  = 10 * time.Minute
+	// loginCookieKeyLabel separates the login cookie's signing key from other
+	// keys derived from the same server secret.
+	loginCookieKeyLabel = "mealquest auth login cookie v1"
+)
+
+// loginState travels from login to callback in the signed login cookie.
+type loginState struct {
+	State    string `json:"s"`
+	Nonce    string `json:"n"`
+	Verifier string `json:"v"`
+	Return   string `json:"r"`
+	Expires  int64  `json:"e"` // Unix seconds
+}
+
+// loginCookie signs and verifies the login cookie with HMAC-SHA256.
+type loginCookie struct {
+	key []byte
+}
+
+func newLoginCookie(secretKey []byte) loginCookie {
+	mac := hmac.New(sha256.New, secretKey)
+	mac.Write([]byte(loginCookieKeyLabel))
+	return loginCookie{key: mac.Sum(nil)}
+}
+
+func (c loginCookie) sign(payload string) string {
+	mac := hmac.New(sha256.New, c.key)
+	mac.Write([]byte(payload))
+	return base64.RawURLEncoding.EncodeToString(mac.Sum(nil))
+}
+
+func (c loginCookie) set(w http.ResponseWriter, s loginState, now time.Time) error {
+	s.Expires = now.Add(loginCookieTTL).Unix()
+	data, err := json.Marshal(s)
+	if err != nil {
+		return err
+	}
+	payload := base64.RawURLEncoding.EncodeToString(data)
+	http.SetCookie(w, &http.Cookie{
+		Name:     loginCookieName,
+		Value:    payload + "." + c.sign(payload),
+		Path:     "/",
+		MaxAge:   int(loginCookieTTL / time.Second),
+		Secure:   true,
+		HttpOnly: true,
+		// Lax so the cookie rides the provider's top-level redirect back.
+		SameSite: http.SameSiteLaxMode,
+	})
+	return nil
+}
+
+func (c loginCookie) clear(w http.ResponseWriter) {
+	http.SetCookie(w, &http.Cookie{
+		Name:     loginCookieName,
+		Path:     "/",
+		MaxAge:   -1,
+		Secure:   true,
+		HttpOnly: true,
+		SameSite: http.SameSiteLaxMode,
+	})
+}
+
+func (c loginCookie) read(r *http.Request, now time.Time) (loginState, error) {
+	cookie, err := r.Cookie(loginCookieName)
+	if err != nil {
+		return loginState{}, errors.New("login cookie missing")
+	}
+	payload, sig, ok := strings.Cut(cookie.Value, ".")
+	if !ok || !hmac.Equal([]byte(sig), []byte(c.sign(payload))) {
+		return loginState{}, errors.New("login cookie signature invalid")
+	}
+	data, err := base64.RawURLEncoding.DecodeString(payload)
+	if err != nil {
+		return loginState{}, fmt.Errorf("login cookie encoding: %w", err)
+	}
+	var s loginState
+	if err := json.Unmarshal(data, &s); err != nil {
+		return loginState{}, fmt.Errorf("login cookie payload: %w", err)
+	}
+	if now.Unix() >= s.Expires {
+		return loginState{}, errors.New("login cookie expired")
+	}
+	return s, nil
+}
+
+// returnPath validates the optional post-login return path. Empty means "/".
+// Only same-origin absolute paths are allowed: no scheme, host, protocol-
+// relative "//" prefix, backslashes or control characters.
+func returnPath(raw string) (string, error) {
+	if raw == "" {
+		return "/", nil
+	}
+	if !strings.HasPrefix(raw, "/") || strings.HasPrefix(raw, "//") || strings.ContainsRune(raw, '\\') {
+		return "", errors.New("return path must be a same-origin path")
+	}
+	for _, c := range raw {
+		if c < 0x20 || c == 0x7f {
+			return "", errors.New("return path contains a control character")
+		}
+	}
+	u, err := url.Parse(raw)
+	if err != nil || u.Scheme != "" || u.Host != "" || u.User != nil {
+		return "", errors.New("return path must be a same-origin path")
+	}
+	return raw, nil
+}

internal/auth/gate_test.go

@@ -0,0 +1,264 @@
+package auth
+
+import (
+	"context"
+	"errors"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/url"
+	"slices"
+	"strings"
+	"testing"
+)
+
+// signInWith completes a login whose ID token has claims edited by edit.
+func (h *harness) signInWith(t *testing.T, edit func(claims map[string]any)) *http.Response {
+	t.Helper()
+	l := h.login(t, LoginPath)
+	c := h.provider.claims(l.query.Get("nonce"))
+	edit(c)
+	return h.callback(l, l.query.Get("state"), h.provider.signRS256(c))
+}
+
+// assertRefused checks resp is the refused-sign-in page and starts no
+// session.
+func assertRefused(t *testing.T, resp *http.Response) {
+	t.Helper()
+	if resp.StatusCode != http.StatusForbidden {
+		t.Fatalf("callback status = %d, want 403", resp.StatusCode)
+	}
+	if ct := resp.Header.Get("Content-Type"); ct != "text/html; charset=utf-8" {
+		t.Errorf("Content-Type = %q, want text/html; charset=utf-8", ct)
+	}
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, want := range []string{
+		"This kitchen is for the household only",
+		`<form method="post" action="/auth/logout">`,
+		"Sign out",
+	} {
+		if !strings.Contains(string(body), want) {
+			t.Errorf("refused page lacks %q:\n%s", want, body)
+		}
+	}
+	for _, c := range resp.Cookies() {
+		// Clearing a session cookie (negative Max-Age) is expected.
+		if (c.Name == SessionCookieName || c.Name == "test_session") && c.MaxAge >= 0 {
+			t.Errorf("refused sign-in set session cookie %s", c.Name)
+		}
+	}
+	assertLoginCookieCleared(t, resp)
+}
+
+func TestGroupGateMember(t *testing.T) {
+	t.Parallel()
+	// Any one allowed group is enough, alongside groups that are not allowed.
+	h := newHarness(t)
+	resp := h.signInWith(t, func(c map[string]any) { c["groups"] = []string{"guests", "mealquest-family"} })
+	if resp.StatusCode != http.StatusSeeOther {
+		t.Fatalf("callback status = %d, want 303", resp.StatusCode)
+	}
+	if started := h.sessions.started(); len(started) != 1 || !slices.Equal(started[0].Groups, []string{"guests", "mealquest-family"}) {
+		t.Errorf("sessions started = %+v, want one with the ID token groups", started)
+	}
+	if n := h.provider.userinfoRequests(); n != 0 {
+		t.Errorf("userinfo requested %d times, want 0 when the ID token has groups", n)
+	}
+}
+
+func TestGroupGateRefused(t *testing.T) {
+	t.Parallel()
+	tests := []struct {
+		name     string
+		groups   any // ID token groups claim; nil removes it
+		userinfo map[string]any
+	}{
+		{name: "non-member", groups: []string{"guests", "MEALQUEST-ADMIN"}},
+		{name: "empty groups claim", groups: []string{}},
+		{name: "groups claim missing from ID token and userinfo", groups: nil},
+		{
+			name:     "non-member in userinfo",
+			groups:   nil,
+			userinfo: map[string]any{"sub": "user-123", "groups": []string{"guests"}},
+		},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			h := newHarness(t)
+			if tc.userinfo != nil {
+				h.provider.setUserinfo(tc.userinfo)
+			}
+			resp := h.signInWith(t, func(c map[string]any) {
+				if tc.groups == nil {
+					delete(c, "groups")
+				} else {
+					c["groups"] = tc.groups
+				}
+			})
+			assertRefused(t, resp)
+			if started := h.sessions.started(); len(started) != 0 {
+				t.Errorf("sessions started = %+v, want none", started)
+			}
+			if !strings.Contains(h.logs.String(), "sign-in refused") {
+				t.Errorf("refusal not logged:\n%s", h.logs.String())
+			}
+		})
+	}
+}
+
+func TestGroupGateUsesUserinfoWhenIDTokenHasNoGroups(t *testing.T) {
+	t.Parallel()
+	h := newHarness(t)
+	h.provider.setUserinfo(map[string]any{"sub": "user-123", "groups": []string{"mealquest-admin"}})
+	resp := h.signInWith(t, func(c map[string]any) { delete(c, "groups") })
+	if resp.StatusCode != http.StatusSeeOther {
+		t.Fatalf("callback status = %d, want 303", resp.StatusCode)
+	}
+	if started := h.sessions.started(); len(started) != 1 || !slices.Equal(started[0].Groups, []string{"mealquest-admin"}) {
+		t.Errorf("sessions started = %+v, want one with the userinfo groups", started)
+	}
+	if n := h.provider.userinfoRequests(); n != 1 {
+		t.Errorf("userinfo requested %d times, want 1", n)
+	}
+}
+
+func TestGroupGateUserinfoFailures(t *testing.T) {
+	t.Parallel()
+	tests := []struct {
+		name     string
+		userinfo map[string]any
+	}{
+		{"subject mismatch", map[string]any{"sub": "someone-else", "groups": []string{"mealquest-admin"}}},
+		{"malformed groups", map[string]any{"sub": "user-123", "groups": "mealquest-admin"}},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			h := newHarness(t)
+			h.provider.setUserinfo(tc.userinfo)
+			resp := h.signInWith(t, func(c map[string]any) { delete(c, "groups") })
+			if resp.StatusCode != http.StatusUnauthorized {
+				t.Errorf("callback status = %d, want 401", resp.StatusCode)
+			}
+			if started := h.sessions.started(); len(started) != 0 {
+				t.Errorf("sessions started = %+v, want none", started)
+			}
+		})
+	}
+}
+
+// A failed userinfo request fails the sign-in without logging the
+// endpoint's response, which may echo credentials.
+func TestGroupGateUserinfoErrorNotLogged(t *testing.T) {
+	t.Parallel()
+	h := newHarness(t)
+	h.provider.mu.Lock()
+	h.provider.userinfoReply = &tokenReply{status: http.StatusInternalServerError, body: `{"error":"leaked-s3cret"}`}
+	h.provider.mu.Unlock()
+	resp := h.signInWith(t, func(c map[string]any) { delete(c, "groups") })
+	if resp.StatusCode != http.StatusUnauthorized {
+		t.Errorf("callback status = %d, want 401", resp.StatusCode)
+	}
+	if started := h.sessions.started(); len(started) != 0 {
+		t.Errorf("sessions started = %+v, want none", started)
+	}
+	logs := h.logs.String()
+	if !strings.Contains(logs, "userinfo") || strings.Contains(logs, "leaked-s3cret") {
+		t.Errorf("logs = %s, want the userinfo failure without the response body", logs)
+	}
+}
+
+// Membership is checked at every login: after removal from the group, the
+// next login is refused and starts no session.
+func TestGroupGateRemovedMemberRefusedAtNextLogin(t *testing.T) {
+	t.Parallel()
+	h := newSessionHarness(t)
+	h.signIn(t)
+	if n := len(h.rows(t)); n != 1 {
+		t.Fatalf("sessions after first login = %d, want 1", n)
+	}
+
+	resp := h.signInWith(t, func(c map[string]any) { c["groups"] = []string{"former-household"} })
+	assertRefused(t, resp)
+	if n := len(h.rows(t)); n != 1 {
+		t.Errorf("sessions after refused login = %d, want still 1", n)
+	}
+}
+
+// A refused sign-in from a browser that still holds a session ends that
+// session and clears its cookie.
+func TestGroupGateRefusalEndsExistingSession(t *testing.T) {
+	t.Parallel()
+	h := newSessionHarness(t)
+	_, cookie := h.signIn(t)
+
+	l := h.login(t, LoginPath)
+	c := h.provider.claims(l.query.Get("nonce"))
+	c["groups"] = []string{"former-household"}
+	code := h.provider.authorize(l.query.Get("code_challenge"), h.provider.signRS256(c))
+	q := url.Values{"code": {code}, "state": {l.query.Get("state")}}
+	resp := h.get(CallbackPath+"?"+q.Encode(), l.cookie, cookie)
+
+	if resp.StatusCode != http.StatusForbidden {
+		t.Fatalf("callback status = %d, want 403", resp.StatusCode)
+	}
+	if n := len(h.rows(t)); n != 0 {
+		t.Errorf("sessions after refused login = %d, want 0", n)
+	}
+	if _, err := h.use(cookie); !errors.Is(err, ErrNoSession) {
+		t.Errorf("old session lookup error = %v, want ErrNoSession", err)
+	}
+	cleared := false
+	for _, c := range resp.Cookies() {
+		cleared = cleared || (c.Name == SessionCookieName && c.MaxAge < 0)
+	}
+	if !cleared {
+		t.Error("refused sign-in did not clear the session cookie")
+	}
+}
+
+func TestGroupGateRefusalEndSessionError(t *testing.T) {
+	t.Parallel()
+	h := newHarness(t)
+	h.sessions.err = errors.New("database down")
+	resp := h.signInWith(t, func(c map[string]any) { c["groups"] = []string{"guests"} })
+	if resp.StatusCode != http.StatusInternalServerError {
+		t.Errorf("callback status = %d, want 500", resp.StatusCode)
+	}
+}
+
+func TestNewRequiresAllowedGroups(t *testing.T) {
+	t.Parallel()
+	p := newFakeProvider(t)
+	_, err := New(context.Background(), Config{
+		Issuer:       p.issuer(),
+		ClientID:     testClientID,
+		ClientSecret: testClientSecret,
+		PublicURL:    testPublicURL,
+		SecretKey:    []byte("k"),
+	}, &memorySessions{}, slog.New(slog.DiscardHandler))
+	if err == nil || !strings.Contains(err.Error(), "allowed group") {
+		t.Errorf("New error = %v, want missing allowed groups named", err)
+	}
+}
+
+func TestNewRequiresUserinfoEndpoint(t *testing.T) {
+	t.Parallel()
+	p := newFakeProvider(t)
+	p.discoveryOverrides = map[string]any{"userinfo_endpoint": nil}
+	_, err := New(context.Background(), Config{
+		Issuer:        p.issuer(),
+		ClientID:      testClientID,
+		ClientSecret:  testClientSecret,
+		PublicURL:     testPublicURL,
+		SecretKey:     []byte("k"),
+		AllowedGroups: testAllowedGroups,
+	}, &memorySessions{}, slog.New(slog.DiscardHandler))
+	if err == nil || !strings.Contains(err.Error(), "userinfo endpoint") {
+		t.Errorf("New error = %v, want the missing userinfo endpoint named", err)
+	}
+}

internal/auth/refused.go

@@ -0,0 +1,37 @@
+package auth
+
+import (
+	"io"
+	"net/http"
+)
+
+// refusedPage is shown when a sign-in succeeds at the provider but the
+// account is not in the household's group. Signing out ends the provider
+// session too, so another account can sign in.
+const refusedPage = `<!doctype html>
+<html lang="en">
+<head>
+<meta charset="utf-8">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<title>MealQuest</title>
+</head>
+<body>
+<main>
+<h1>This kitchen is for the household only</h1>
+<p>The account you signed in with is not part of our kitchen.</p>
+<form method="post" action="` + LogoutPath + `">
+<button type="submit">Sign out</button>
+</form>
+</main>
+</body>
+</html>
+`
+
+// refuse writes the refused-sign-in page with 403.
+func (a *Auth) refuse(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	w.WriteHeader(http.StatusForbidden)
+	if _, err := io.WriteString(w, refusedPage); err != nil {
+		a.logger.WarnContext(r.Context(), "write refused sign-in page", "error", err)
+	}
+}

internal/auth/session.go

@@ -0,0 +1,238 @@
+package auth
+
+import (
+	"crypto/rand"
+	"crypto/sha256"
+	"database/sql"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"time"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/store"
+)
+
+// SessionCookieName is the session cookie. The __Host- prefix makes the
+// browser insist on Secure, Path=/ and no Domain.
+const SessionCookieName = "__Host-mealquest_session"
+
+// sessionIDBytes is the size of the random session ID: 256 bits.
+const sessionIDBytes = 32
+
+// ErrNoSession means the request carries no live session: the cookie is
+// missing or malformed, or its session is unknown, ended or expired.
+var ErrNoSession = errors.New("auth: no valid session")
+
+// Session is a signed-in household member's server-side session.
+type Session struct {
+	Subject   string
+	Email     string
+	Name      string
+	Groups    []string
+	CSRFToken string
+	CreatedAt time.Time
+	// LastSeenAt is the last time the session was used.
+	LastSeenAt time.Time
+	// ExpiresAt is when the session ends unless used again first.
+	ExpiresAt time.Time
+}
+
+// SessionManager keeps sessions in the sessions table. The cookie holds only
+// the random session ID; the table holds only its SHA-256 hash. A session
+// ends after idle without use and always max after it was created.
+type SessionManager struct {
+	db   *store.Store
+	idle time.Duration
+	max  time.Duration
+	// now is the clock; tests replace it.
+	now func() time.Time
+}
+
+// NewSessionManager returns a SessionManager over db. idle and max must be
+// positive with max >= idle.
+func NewSessionManager(db *store.Store, idle, max time.Duration) (*SessionManager, error) {
+	switch {
+	case db == nil:
+		return nil, errors.New("auth: session store is required")
+	case idle <= 0 || max <= 0:
+		return nil, errors.New("auth: session idle and max lifetimes must be positive")
+	case max < idle:
+		return nil, errors.New("auth: session max lifetime must be at least the idle lifetime")
+	}
+	return &SessionManager{db: db, idle: idle, max: max, now: time.Now}, nil
+}
+
+// StartSession creates a session for claims and sets the session cookie.
+func (m *SessionManager) StartSession(w http.ResponseWriter, r *http.Request, claims Claims) error {
+	if claims.Subject == "" {
+		return errors.New("auth: session needs a subject")
+	}
+	id, csrf := randomToken(), randomToken()
+	groups := claims.Groups
+	if groups == nil {
+		groups = []string{}
+	}
+	groupsJSON, err := json.Marshal(groups)
+	if err != nil {
+		return fmt.Errorf("auth: encode session groups: %w", err)
+	}
+
+	now := m.timestamp()
+	if _, err := m.db.Writer.ExecContext(r.Context(), `
+		INSERT INTO sessions (id_hash, subject, email, name, groups, csrf_token, created_at, last_seen_at, expires_at)
+		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)`,
+		hashSessionID(id), claims.Subject, claims.Email, claims.Name, string(groupsJSON), csrf,
+		now, now, m.expiry(now.Time, now.Time),
+	); err != nil {
+		return fmt.Errorf("auth: create session: %w", err)
+	}
+
+	// The cookie outlives idle gaps so a returning device presents its ID;
+	// the server decides whether the session is still live. Max-Age is whole
+	// seconds, rounded up so the cookie never ends before the absolute limit.
+	http.SetCookie(w, sessionCookie(id, cookieMaxAge(m.max)))
+	return nil
+}
+
+// cookieMaxAge is lifetime in whole seconds, rounded up. It rounds the
+// quotient rather than adding to lifetime, which would overflow near the
+// largest time.Duration.
+func cookieMaxAge(lifetime time.Duration) int {
+	seconds := lifetime / time.Second
+	if lifetime%time.Second != 0 {
+		seconds++
+	}
+	return int(seconds)
+}
+
+// SessionFor returns the live session r carries and slides its last use to
+// now. It returns ErrNoSession when there is none; an expired session is
+// deleted.
+func (m *SessionManager) SessionFor(r *http.Request) (Session, error) {
+	idHash, err := sessionIDHash(r)
+	if err != nil {
+		return Session{}, err
+	}
+	now := m.timestamp()
+
+	var s Session
+	live := false
+	err = m.db.WithTx(r.Context(), func(tx *sql.Tx) error {
+		var groupsJSON string
+		var created, lastSeen, expires store.Timestamp
+		err := tx.QueryRowContext(r.Context(), `
+			SELECT subject, email, name, groups, csrf_token, created_at, last_seen_at, expires_at
+			FROM sessions WHERE id_hash = ?`, idHash,
+		).Scan(&s.Subject, &s.Email, &s.Name, &groupsJSON, &s.CSRFToken, &created, &lastSeen, &expires)
+		if errors.Is(err, sql.ErrNoRows) {
+			return nil
+		}
+		if err != nil {
+			return fmt.Errorf("auth: read session: %w", err)
+		}
+
+		if !now.Before(expires.Time) || now.Sub(lastSeen.Time) >= m.idle || now.Sub(created.Time) >= m.max {
+			if _, err := tx.ExecContext(r.Context(), `DELETE FROM sessions WHERE id_hash = ?`, idHash); err != nil {
+				return fmt.Errorf("auth: delete expired session: %w", err)
+			}
+			return nil
+		}
+
+		if err := json.Unmarshal([]byte(groupsJSON), &s.Groups); err != nil {
+			return fmt.Errorf("auth: decode session groups: %w", err)
+		}
+		expiresAt := m.expiry(created.Time, now.Time)
+		if _, err := tx.ExecContext(r.Context(), `
+			UPDATE sessions SET last_seen_at = ?, expires_at = ? WHERE id_hash = ?`,
+			now, expiresAt, idHash,
+		); err != nil {
+			return fmt.Errorf("auth: slide session: %w", err)
+		}
+		s.CreatedAt, s.LastSeenAt, s.ExpiresAt = created.Time, now.Time, expiresAt.Time
+		live = true
+		return nil
+	})
+	if err != nil {
+		return Session{}, err
+	}
+	if !live {
+		return Session{}, ErrNoSession
+	}
+	return s, nil
+}
+
+// EndSession deletes the session r carries, if any, and clears the cookie.
+func (m *SessionManager) EndSession(w http.ResponseWriter, r *http.Request) error {
+	http.SetCookie(w, sessionCookie("", -1))
+	idHash, err := sessionIDHash(r)
+	if errors.Is(err, ErrNoSession) {
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+	if _, err := m.db.Writer.ExecContext(r.Context(), `DELETE FROM sessions WHERE id_hash = ?`, idHash); err != nil {
+		return fmt.Errorf("auth: delete session: %w", err)
+	}
+	return nil
+}
+
+// timestamp is the clock's current instant at stored precision.
+func (m *SessionManager) timestamp() store.Timestamp {
+	return store.Timestamp{Time: m.now().UTC().Truncate(time.Millisecond)}
+}
+
+// expiry is when a session created at created and last used at lastSeen
+// ends: idle after lastSeen, but never later than max after created.
+func (m *SessionManager) expiry(created, lastSeen time.Time) store.Timestamp {
+	idle, absolute := lastSeen.Add(m.idle), created.Add(m.max)
+	if absolute.Before(idle) {
+		return store.Timestamp{Time: absolute}
+	}
+	return store.Timestamp{Time: idle}
+}
+
+// sessionCookie is the session cookie carrying value, with maxAge seconds;
+// a negative maxAge clears it.
+func sessionCookie(value string, maxAge int) *http.Cookie {
+	return &http.Cookie{
+		Name:     SessionCookieName,
+		Value:    value,
+		Path:     "/",
+		MaxAge:   maxAge,
+		Secure:   true,
+		HttpOnly: true,
+		SameSite: http.SameSiteLaxMode,
+	}
+}
+
+// sessionIDHash returns the stored hash of r's session ID, or ErrNoSession
+// when the cookie is missing or is not a well-formed ID.
+func sessionIDHash(r *http.Request) (string, error) {
+	c, err := r.Cookie(SessionCookieName)
+	if err != nil {
+		return "", ErrNoSession
+	}
+	raw, err := base64.RawURLEncoding.DecodeString(c.Value)
+	if err != nil || len(raw) != sessionIDBytes {
+		return "", ErrNoSession
+	}
+	return hashSessionID(c.Value), nil
+}
+
+// hashSessionID is the SHA-256 hex digest of the cookie value.
+func hashSessionID(id string) string {
+	sum := sha256.Sum256([]byte(id))
+	return hex.EncodeToString(sum[:])
+}
+
+// randomToken returns 256 random bits, base64url-encoded without padding.
+// crypto/rand.Read never returns an error; it crashes the program instead.
+func randomToken() string {
+	b := make([]byte, sessionIDBytes)
+	rand.Read(b)
+	return base64.RawURLEncoding.EncodeToString(b)
+}

internal/auth/session_test.go

@@ -0,0 +1,523 @@
+package auth
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"errors"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"slices"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/go-chi/chi/v5"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/store"
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/migrations"
+)
+
+const (
+	testIdle = 30 * 24 * time.Hour
+	testMax  = 180 * 24 * time.Hour
+)
+
+// testEpoch is the fake clock's starting instant.
+var testEpoch = time.Date(2026, 10, 3, 18, 30, 0, 0, time.UTC)
+
+// sessionHarness runs the real login flow against a fake provider with a
+// SessionManager over a migrated database and a fake clock.
+type sessionHarness struct {
+	*harness
+	db       *store.Store
+	sessions *SessionManager
+	auth     *Auth
+	clock    time.Time
+}
+
+func newSessionHarness(t *testing.T) *sessionHarness {
+	t.Helper()
+	ctx := context.Background()
+	db, err := store.Open(ctx, t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := db.Close(); err != nil {
+			t.Error(err)
+		}
+	})
+	if err := store.Migrate(ctx, db.Writer, migrations.FS); err != nil {
+		t.Fatal(err)
+	}
+	sessions, err := NewSessionManager(db, testIdle, testMax)
+	if err != nil {
+		t.Fatal(err)
+	}
+	h := &sessionHarness{db: db, sessions: sessions, clock: testEpoch}
+	sessions.now = func() time.Time { return h.clock }
+
+	p := newFakeProvider(t)
+	logs := &syncBuffer{}
+	a, err := New(ctx, Config{
+		Issuer:        p.issuer(),
+		ClientID:      testClientID,
+		ClientSecret:  testClientSecret,
+		PublicURL:     testPublicURL,
+		SecretKey:     []byte("server-secret-key"),
+		AllowedGroups: testAllowedGroups,
+	}, sessions, slog.New(slog.NewTextHandler(logs, nil)))
+	if err != nil {
+		t.Fatal(err)
+	}
+	r := chi.NewRouter()
+	a.Mount(r)
+	h.harness = &harness{provider: p, router: r, logs: logs}
+	h.auth = a
+	return h
+}
+
+func (h *sessionHarness) advance(d time.Duration) { h.clock = h.clock.Add(d) }
+
+// signIn completes a login and returns the callback response and the
+// session cookie it set.
+func (h *sessionHarness) signIn(t *testing.T) (*http.Response, *http.Cookie) {
+	t.Helper()
+	l := h.login(t, LoginPath)
+	resp := h.callback(l, l.query.Get("state"), h.provider.signRS256(h.provider.claims(l.query.Get("nonce"))))
+	if resp.StatusCode != http.StatusSeeOther {
+		t.Fatalf("callback status = %d, want 303", resp.StatusCode)
+	}
+	for _, c := range resp.Cookies() {
+		if c.Name == SessionCookieName {
+			return resp, c
+		}
+	}
+	t.Fatalf("callback set no %s cookie", SessionCookieName)
+	return nil, nil
+}
+
+// use looks up the session cookie c names.
+func (h *sessionHarness) use(c *http.Cookie) (Session, error) {
+	req := httptest.NewRequest(http.MethodGet, "/api/anything", nil)
+	if c != nil {
+		req.AddCookie(c)
+	}
+	return h.sessions.SessionFor(req)
+}
+
+type sessionRow struct {
+	idHash, subject, email, name, groups, csrf string
+	created, lastSeen, expires                 store.Timestamp
+}
+
+func (h *sessionHarness) rows(t *testing.T) []sessionRow {
+	t.Helper()
+	rs, err := h.db.Reader.Query(`SELECT id_hash, subject, email, name, groups, csrf_token,
+		created_at, last_seen_at, expires_at FROM sessions`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer rs.Close()
+	var out []sessionRow
+	for rs.Next() {
+		var r sessionRow
+		if err := rs.Scan(&r.idHash, &r.subject, &r.email, &r.name, &r.groups, &r.csrf,
+			&r.created, &r.lastSeen, &r.expires); err != nil {
+			t.Fatal(err)
+		}
+		out = append(out, r)
+	}
+	if err := rs.Err(); err != nil {
+		t.Fatal(err)
+	}
+	return out
+}
+
+// sessionSetCookie returns the raw Set-Cookie header for the session cookie.
+func sessionSetCookie(t *testing.T, resp *http.Response) string {
+	t.Helper()
+	for _, v := range resp.Header.Values("Set-Cookie") {
+		if strings.HasPrefix(v, SessionCookieName+"=") {
+			return v
+		}
+	}
+	t.Fatalf("no Set-Cookie for %s in %q", SessionCookieName, resp.Header.Values("Set-Cookie"))
+	return ""
+}
+
+// assertSessionCookieAttributes checks the attributes the __Host- prefix
+// and D-004 require, on the raw header so nothing is lost in parsing.
+func assertSessionCookieAttributes(t *testing.T, raw string) {
+	t.Helper()
+	attrs := map[string]bool{}
+	for _, a := range strings.Split(raw, ";")[1:] {
+		name, _, _ := strings.Cut(strings.TrimSpace(a), "=")
+		attrs[strings.ToLower(name)] = true
+	}
+	for _, want := range []string{"Path=/", "HttpOnly", "Secure", "SameSite=Lax"} {
+		if !slices.Contains(strings.Split(raw, "; "), want) {
+			t.Errorf("session Set-Cookie %q lacks %s", raw, want)
+		}
+	}
+	if attrs["domain"] {
+		t.Errorf("session Set-Cookie %q has a Domain", raw)
+	}
+}
+
+func sha256Hex(s string) string {
+	sum := sha256.Sum256([]byte(s))
+	return hex.EncodeToString(sum[:])
+}
+
+func TestCallbackStartsSession(t *testing.T) {
+	t.Parallel()
+	h := newSessionHarness(t)
+	resp, cookie := h.signIn(t)
+
+	assertSessionCookieAttributes(t, sessionSetCookie(t, resp))
+	if cookie.MaxAge != int(testMax/time.Second) {
+		t.Errorf("session cookie MaxAge = %d, want %d", cookie.MaxAge, int(testMax/time.Second))
+	}
+
+	rows := h.rows(t)
+	if len(rows) != 1 {
+		t.Fatalf("sessions has %d rows, want 1", len(rows))
+	}
+	r := rows[0]
+	if len(cookie.Value) != 43 {
+		t.Errorf("session ID %q is %d chars, want 43 (256 bits, base64url)", cookie.Value, len(cookie.Value))
+	}
+	if r.idHash != sha256Hex(cookie.Value) {
+		t.Errorf("id_hash = %q, want the SHA-256 of the cookie value", r.idHash)
+	}
+	if r.subject != "user-123" || r.email != "cook@example.com" || r.name != "Home Cook" ||
+		r.groups != `["mealquest-admin"]` {
+		t.Errorf("session row = %+v, want the ID token claims", r)
+	}
+	if len(r.csrf) != 43 || r.csrf == cookie.Value {
+		t.Errorf("csrf_token = %q, want a separate 256-bit token", r.csrf)
+	}
+	if !r.created.Equal(testEpoch) || !r.lastSeen.Equal(testEpoch) || !r.expires.Equal(testEpoch.Add(testIdle)) {
+		t.Errorf("created, last_seen, expires = %v, %v, %v, want %v, %v, %v",
+			r.created, r.lastSeen, r.expires, testEpoch, testEpoch, testEpoch.Add(testIdle))
+	}
+
+	s, err := h.use(cookie)
+	if err != nil {
+		t.Fatalf("SessionFor = %v, want the new session", err)
+	}
+	if s.Subject != "user-123" || s.CSRFToken != r.csrf || !slices.Equal(s.Groups, []string{"mealquest-admin"}) {
+		t.Errorf("SessionFor = %+v", s)
+	}
+}
+
+func TestStartSessionStoresOnlyTheHash(t *testing.T) {
+	t.Parallel()
+	h := newSessionHarness(t)
+	_, cookie := h.signIn(t)
+	var n int
+	err := h.db.Reader.QueryRow(`SELECT count(*) FROM sessions WHERE
+		id_hash = ?1 OR subject = ?1 OR email = ?1 OR name = ?1 OR groups = ?1 OR csrf_token = ?1`,
+		cookie.Value).Scan(&n)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 0 {
+		t.Error("the raw session ID is stored in the sessions table")
+	}
+}
+
+func TestSessionLastSeenSlides(t *testing.T) {
+	t.Parallel()
+	h := newSessionHarness(t)
+	_, cookie := h.signIn(t)
+
+	// Used every 20 days, the session outlives several idle periods.
+	for range 4 {
+		h.advance(20 * 24 * time.Hour)
+		s, err := h.use(cookie)
+		if err != nil {
+			t.Fatalf("at %v SessionFor = %v, want the session", h.clock, err)
+		}
+		if !s.LastSeenAt.Equal(h.clock) || !s.ExpiresAt.Equal(h.clock.Add(testIdle)) {
+			t.Errorf("at %v session last seen %v, expires %v, want %v, %v",
+				h.clock, s.LastSeenAt, s.ExpiresAt, h.clock, h.clock.Add(testIdle))
+		}
+		r := h.rows(t)[0]
+		if !r.lastSeen.Equal(h.clock) || !r.expires.Equal(h.clock.Add(testIdle)) || !r.created.Equal(testEpoch) {
+			t.Errorf("at %v row created %v, last seen %v, expires %v", h.clock, r.created, r.lastSeen, r.expires)
+		}
+	}
+}
+
+func TestSessionIdleExpiry(t *testing.T) {
+	t.Parallel()
+	h := newSessionHarness(t)
+	_, cookie := h.signIn(t)
+
+	h.advance(testIdle - time.Millisecond)
+	if _, err := h.use(cookie); err != nil {
+		t.Fatalf("just inside the idle limit SessionFor = %v, want the session", err)
+	}
+	h.advance(testIdle)
+	if _, err := h.use(cookie); !errors.Is(err, ErrNoSession) {
+		t.Fatalf("after idle SessionFor = %v, want ErrNoSession", err)
+	}
+	if n := len(h.rows(t)); n != 0 {
+		t.Errorf("expired session left %d rows, want 0", n)
+	}
+	// Turning the clock back cannot revive it.
+	h.clock = testEpoch
+	if _, err := h.use(cookie); !errors.Is(err, ErrNoSession) {
+		t.Errorf("after deletion SessionFor = %v, want ErrNoSession", err)
+	}
+}
+
+func TestSessionAbsoluteExpiry(t *testing.T) {
+	t.Parallel()
+	h := newSessionHarness(t)
+	_, cookie := h.signIn(t)
+
+	for h.clock.Before(testEpoch.Add(testMax - 20*24*time.Hour)) {
+		h.advance(20 * 24 * time.Hour)
+		if _, err := h.use(cookie); err != nil {
+			t.Fatalf("at %v SessionFor = %v, want the session", h.clock, err)
+		}
+	}
+	// Last used 20 days before the absolute limit: the idle window would run
+	// past it, so expiry is capped there.
+	if r := h.rows(t)[0]; !r.expires.Equal(testEpoch.Add(testMax)) {
+		t.Errorf("expires_at = %v, want the absolute limit %v", r.expires, testEpoch.Add(testMax))
+	}
+
+	h.clock = testEpoch.Add(testMax - time.Millisecond)
+	if _, err := h.use(cookie); err != nil {
+		t.Fatalf("just inside the absolute limit SessionFor = %v, want the session", err)
+	}
+	h.clock = testEpoch.Add(testMax)
+	if _, err := h.use(cookie); !errors.Is(err, ErrNoSession) {
+		t.Fatalf("at the absolute limit, used 1ms ago, SessionFor = %v, want ErrNoSession", err)
+	}
+	if n := len(h.rows(t)); n != 0 {
+		t.Errorf("expired session left %d rows, want 0", n)
+	}
+}
+
+// A max with fractional seconds rounds the cookie Max-Age up, so the browser
+// keeps the cookie until the server-side absolute limit.
+func TestSessionCookieOutlivesFractionalMax(t *testing.T) {
+	t.Parallel()
+	h := newSessionHarness(t)
+	h.sessions.idle, h.sessions.max = 1500*time.Millisecond, 2500*time.Millisecond
+	_, cookie := h.signIn(t)
+	if cookie.MaxAge != 3 {
+		t.Errorf("session cookie MaxAge = %d, want 3", cookie.MaxAge)
+	}
+	if r := h.rows(t)[0]; !r.expires.Equal(testEpoch.Add(1500 * time.Millisecond)) {
+		t.Errorf("expires_at = %v, want %v", r.expires, testEpoch.Add(1500*time.Millisecond))
+	}
+
+	h.advance(time.Second)
+	if _, err := h.use(cookie); err != nil {
+		t.Fatalf("at 1s SessionFor = %v, want the session", err)
+	}
+	h.clock = testEpoch.Add(2500*time.Millisecond - time.Millisecond)
+	if _, err := h.use(cookie); err != nil {
+		t.Fatalf("just inside the absolute limit SessionFor = %v, want the session", err)
+	}
+	h.clock = testEpoch.Add(2500 * time.Millisecond)
+	if _, err := h.use(cookie); !errors.Is(err, ErrNoSession) {
+		t.Errorf("at the absolute limit SessionFor = %v, want ErrNoSession", err)
+	}
+}
+
+// A lifetime near the largest accepted duration still yields a positive,
+// rounded-up cookie Max-Age rather than overflowing.
+func TestSessionCookieMaxAgeNearLargestMax(t *testing.T) {
+	t.Parallel()
+	largest, err := time.ParseDuration("2562047h47m16.854s")
+	if err != nil {
+		t.Fatal(err)
+	}
+	h := newSessionHarness(t)
+	h.sessions.max = largest
+	_, cookie := h.signIn(t)
+	if want := 9223372037; cookie.MaxAge != want {
+		t.Errorf("session cookie MaxAge = %d, want %d", cookie.MaxAge, want)
+	}
+}
+
+// A lifetime shortened by configuration applies to existing sessions even
+// though their stored expires_at is later.
+func TestSessionLifetimeChecksUseCurrentConfig(t *testing.T) {
+	t.Parallel()
+	h := newSessionHarness(t)
+	_, cookie := h.signIn(t)
+	h.sessions.idle = 24 * time.Hour
+	h.advance(24 * time.Hour)
+	if _, err := h.use(cookie); !errors.Is(err, ErrNoSession) {
+		t.Errorf("past the shortened idle SessionFor = %v, want ErrNoSession", err)
+	}
+
+	_, cookie = h.signIn(t)
+	h.sessions.idle, h.sessions.max = 24*time.Hour, 48*time.Hour
+	for range 3 {
+		h.advance(12 * time.Hour)
+		if _, err := h.use(cookie); err != nil {
+			t.Fatalf("SessionFor = %v, want the session", err)
+		}
+	}
+	h.advance(12 * time.Hour)
+	if _, err := h.use(cookie); !errors.Is(err, ErrNoSession) {
+		t.Errorf("past the shortened max SessionFor = %v, want ErrNoSession", err)
+	}
+
+	// Used recently and with expires_at still ahead, but older than a max
+	// shortened after that use: only the absolute check ends it.
+	h.sessions.idle, h.sessions.max = testIdle, testMax
+	_, cookie = h.signIn(t)
+	h.advance(10 * 24 * time.Hour)
+	if _, err := h.use(cookie); err != nil {
+		t.Fatalf("SessionFor = %v, want the session", err)
+	}
+	h.sessions.max = 10 * 24 * time.Hour
+	h.advance(time.Hour)
+	if _, err := h.use(cookie); !errors.Is(err, ErrNoSession) {
+		t.Errorf("past a max shortened after the last use SessionFor = %v, want ErrNoSession", err)
+	}
+}
+
+func TestSessionForRejectsBadCookies(t *testing.T) {
+	t.Parallel()
+	h := newSessionHarness(t)
+	h.signIn(t)
+	for name, c := range map[string]*http.Cookie{
+		"missing":      nil,
+		"empty":        {Name: SessionCookieName, Value: ""},
+		"not base64":   {Name: SessionCookieName, Value: strings.Repeat("!", 43)},
+		"short":        {Name: SessionCookieName, Value: "AAAA"},
+		"unknown ID":   {Name: SessionCookieName, Value: randomToken()},
+		"other cookie": {Name: "mealquest_session", Value: randomToken()},
+	} {
+		if _, err := h.use(c); !errors.Is(err, ErrNoSession) {
+			t.Errorf("%s: SessionFor = %v, want ErrNoSession", name, err)
+		}
+	}
+	if n := len(h.rows(t)); n != 1 {
+		t.Errorf("sessions has %d rows, want the signed-in session only", n)
+	}
+}
+
+func (h *sessionHarness) logout(cookies ...*http.Cookie) *http.Response {
+	req := httptest.NewRequest(http.MethodPost, LogoutPath, nil)
+	for _, c := range cookies {
+		req.AddCookie(c)
+	}
+	rec := httptest.NewRecorder()
+	h.router.ServeHTTP(rec, req)
+	return rec.Result()
+}
+
+func TestLogout(t *testing.T) {
+	t.Parallel()
+	h := newSessionHarness(t)
+	_, cookie := h.signIn(t)
+	_, other := h.signIn(t)
+
+	resp := h.logout(cookie)
+	if resp.StatusCode != http.StatusSeeOther {
+		t.Fatalf("logout status = %d, want 303", resp.StatusCode)
+	}
+	want := h.provider.issuer() + "/end-session/"
+	if got := resp.Header.Get("Location"); got != want || h.auth.EndSessionURL() != want {
+		t.Errorf("logout redirect = %q, EndSessionURL = %q, want %q", got, h.auth.EndSessionURL(), want)
+	}
+	raw := sessionSetCookie(t, resp)
+	assertSessionCookieAttributes(t, raw)
+	if !strings.HasPrefix(raw, SessionCookieName+"=;") || !strings.Contains(raw, "Max-Age=0") {
+		t.Errorf("logout Set-Cookie = %q, want the cookie cleared", raw)
+	}
+
+	rows := h.rows(t)
+	if len(rows) != 1 || rows[0].idHash != sha256Hex(other.Value) {
+		t.Errorf("after logout sessions = %+v, want only the other session", rows)
+	}
+	if _, err := h.use(cookie); !errors.Is(err, ErrNoSession) {
+		t.Errorf("logged-out cookie: SessionFor = %v, want ErrNoSession", err)
+	}
+	if _, err := h.use(other); err != nil {
+		t.Errorf("other session: SessionFor = %v, want it untouched", err)
+	}
+}
+
+func TestLogoutWithoutSession(t *testing.T) {
+	t.Parallel()
+	h := newSessionHarness(t)
+	resp := h.logout()
+	if resp.StatusCode != http.StatusSeeOther || resp.Header.Get("Location") != h.provider.issuer()+"/end-session/" {
+		t.Errorf("logout = %d to %q, want 303 to the end session endpoint", resp.StatusCode, resp.Header.Get("Location"))
+	}
+	assertSessionCookieAttributes(t, sessionSetCookie(t, resp))
+}
+
+func TestLogoutIsPostOnly(t *testing.T) {
+	t.Parallel()
+	h := newSessionHarness(t)
+	_, cookie := h.signIn(t)
+	if resp := h.get(LogoutPath, cookie); resp.StatusCode != http.StatusMethodNotAllowed {
+		t.Errorf("GET %s status = %d, want 405", LogoutPath, resp.StatusCode)
+	}
+	if _, err := h.use(cookie); err != nil {
+		t.Errorf("after GET %s SessionFor = %v, want the session", LogoutPath, err)
+	}
+}
+
+func TestLogoutSessionError(t *testing.T) {
+	t.Parallel()
+	h := newHarness(t)
+	h.sessions.err = errors.New("database down")
+	rec := httptest.NewRecorder()
+	h.router.ServeHTTP(rec, httptest.NewRequest(http.MethodPost, LogoutPath, nil))
+	if rec.Code != http.StatusInternalServerError {
+		t.Errorf("logout status = %d, want 500", rec.Code)
+	}
+}
+
+func TestNewRequiresEndSessionEndpoint(t *testing.T) {
+	t.Parallel()
+	p := newFakeProvider(t)
+	p.discoveryOverrides = map[string]any{"end_session_endpoint": nil}
+	_, err := New(context.Background(), Config{
+		Issuer:        p.issuer(),
+		ClientID:      testClientID,
+		ClientSecret:  testClientSecret,
+		PublicURL:     testPublicURL,
+		SecretKey:     []byte("k"),
+		AllowedGroups: testAllowedGroups,
+	}, &memorySessions{}, slog.New(slog.DiscardHandler))
+	if err == nil || !strings.Contains(err.Error(), "end session endpoint") {
+		t.Errorf("New error = %v, want the missing end session endpoint named", err)
+	}
+}
+
+func TestNewSessionManagerValidates(t *testing.T) {
+	t.Parallel()
+	db := &store.Store{}
+	for _, tc := range []struct {
+		name      string
+		db        *store.Store
+		idle, max time.Duration
+	}{
+		{"nil store", nil, time.Hour, time.Hour},
+		{"zero idle", db, 0, time.Hour},
+		{"negative max", db, time.Hour, -time.Hour},
+		{"max below idle", db, 2 * time.Hour, time.Hour},
+	} {
+		if _, err := NewSessionManager(tc.db, tc.idle, tc.max); err == nil {
+			t.Errorf("%s: NewSessionManager succeeded", tc.name)
+		}
+	}
+}

internal/config/config.go

@@ -11,6 +11,9 @@ import (
 	"strconv"
 	"strings"
 	"time"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/forwarded"
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/secureurl"
 )
 
 // Environment variable names.
@@ -20,6 +23,23 @@ const (
 	EnvDataDir         = "MEALQUEST_DATA_DIR"
 	EnvShutdownTimeout = "MEALQUEST_SHUTDOWN_TIMEOUT"
 	EnvSecretKeyFile   = "MEALQUEST_SECRET_KEY_FILE"
+
+	EnvOIDCIssuer           = "MEALQUEST_OIDC_ISSUER"
+	EnvOIDCClientID         = "MEALQUEST_OIDC_CLIENT_ID"
+	EnvOIDCClientSecretFile = "MEALQUEST_OIDC_CLIENT_SECRET_FILE"
+	EnvOIDCAllowedGroups    = "MEALQUEST_OIDC_ALLOWED_GROUPS"
+
+	EnvSessionIdle = "MEALQUEST_SESSION_IDLE"
+	EnvSessionMax  = "MEALQUEST_SESSION_MAX"
+
+	EnvTrustedProxy = "MEALQUEST_TRUSTED_PROXY"
+)
+
+// Session lifetime defaults (D-004): long enough that the kitchen tablet
+// stays signed in.
+const (
+	DefaultSessionIdle = 720 * time.Hour  // 30 days
+	DefaultSessionMax  = 4320 * time.Hour // 180 days
 )
 
 // Config is the validated service configuration.
@@ -29,6 +49,22 @@ type Config struct {
 	DataDir         string
 	ShutdownTimeout time.Duration
 	SecretKey       Secret
+
+	// OIDCIssuer is the Authentik issuer URL used for discovery.
+	OIDCIssuer       *url.URL
+	OIDCClientID     string
+	OIDCClientSecret Secret
+	// OIDCAllowedGroups lists the groups whose members may sign in.
+	OIDCAllowedGroups []string
+
+	// SessionIdle ends a session left unused this long.
+	SessionIdle time.Duration
+	// SessionMax ends every session this long after sign-in, used or not.
+	SessionMax time.Duration
+
+	// TrustedProxy lists the reverse proxies whose X-Forwarded-For and
+	// X-Forwarded-Proto headers are honoured. Empty trusts no peer.
+	TrustedProxy forwarded.Trusted
 }
 
 // PublicOrigin returns the scheme and host of PublicURL, the only parts of it
@@ -47,10 +83,23 @@ func load(lookup func(string) (string, bool)) (Config, error) {
 	r := reader{lookup: lookup}
 	cfg := Config{
 		HTTPAddr:        r.listenAddr(EnvHTTPAddr),
-		PublicURL:       r.httpURL(EnvPublicURL),
+		PublicURL:       r.secureURL(EnvPublicURL),
 		DataDir:         r.dir(EnvDataDir),
 		ShutdownTimeout: r.duration(EnvShutdownTimeout),
 		SecretKey:       r.secretFile(EnvSecretKeyFile),
+
+		OIDCIssuer:        r.secureURL(EnvOIDCIssuer),
+		OIDCClientID:      r.str(EnvOIDCClientID),
+		OIDCClientSecret:  r.secretFile(EnvOIDCClientSecretFile),
+		OIDCAllowedGroups: r.list(EnvOIDCAllowedGroups),
+
+		SessionIdle: r.sessionDuration(EnvSessionIdle, DefaultSessionIdle),
+		SessionMax:  r.sessionDuration(EnvSessionMax, DefaultSessionMax),
+
+		TrustedProxy: r.trustedProxy(EnvTrustedProxy),
+	}
+	if cfg.SessionIdle > 0 && cfg.SessionMax > 0 && cfg.SessionMax < cfg.SessionIdle {
+		r.fail(EnvSessionMax, "must be at least %s (%s)", EnvSessionIdle, cfg.SessionIdle)
 	}
 	if len(r.problems) > 0 {
 		return Config{}, &Error{Problems: r.problems}
@@ -114,6 +163,41 @@ func (r *reader) required(name string) (string, bool) {
 	return v, true
 }
 
+func (r *reader) str(name string) string {
+	v, _ := r.required(name)
+	return v
+}
+
+// list parses a comma-separated list. Every entry must be non-empty after
+// trimming spaces.
+func (r *reader) list(name string) []string {
+	v, ok := r.required(name)
+	if !ok {
+		return nil
+	}
+	items := strings.Split(v, ",")
+	for i, item := range items {
+		items[i] = strings.TrimSpace(item)
+		if items[i] == "" {
+			r.fail(name, "empty entry in comma-separated list %q", v)
+			return nil
+		}
+	}
+	return items
+}
+
+// trustedProxy parses an optional comma-separated list of IP addresses and
+// CIDR prefixes with forwarded.ParseTrusted. Unset or blank trusts no peer.
+func (r *reader) trustedProxy(name string) forwarded.Trusted {
+	v, _ := r.lookup(name)
+	t, err := forwarded.ParseTrusted(v)
+	if err != nil {
+		r.fail(name, "%v", err)
+		return nil
+	}
+	return t
+}
+
 func (r *reader) listenAddr(name string) string {
 	v, ok := r.required(name)
 	if !ok {
@@ -155,15 +239,21 @@ func validHostname(h string) bool {
 	return true
 }
 
-func (r *reader) httpURL(name string) *url.URL {
+// secureURL reads an absolute URL that must pass secureurl.Check: https://,
+// or http:// to a loopback host only.
+func (r *reader) secureURL(name string) *url.URL {
 	v, ok := r.required(name)
 	if !ok {
 		return nil
 	}
 	// The value is never echoed: it may carry credentials.
 	u, err := url.Parse(v)
-	if err != nil || (u.Scheme != "http" && u.Scheme != "https") || u.Hostname() == "" {
-		r.fail(name, "invalid URL (want absolute http:// or https:// URL)")
+	if err != nil {
+		r.fail(name, "invalid URL (want absolute https:// URL)")
+		return nil
+	}
+	if err := secureurl.Check(u); err != nil {
+		r.fail(name, "invalid URL: %v", err)
 		return nil
 	}
 	if u.User != nil {
@@ -195,6 +285,32 @@ func (r *reader) duration(name string) time.Duration {
 	if !ok {
 		return 0
 	}
+	return r.parseDuration(name, v)
+}
+
+// optionalDuration returns def when name is unset. A set value, even an empty
+// one, must be a valid positive duration.
+func (r *reader) optionalDuration(name string, def time.Duration) time.Duration {
+	v, ok := r.lookup(name)
+	if !ok {
+		return def
+	}
+	return r.parseDuration(name, v)
+}
+
+// sessionDuration is optionalDuration restricted to whole milliseconds:
+// session expiry is stored as a store.Timestamp, which keeps millisecond
+// precision, so a finer duration could not be honoured.
+func (r *reader) sessionDuration(name string, def time.Duration) time.Duration {
+	d := r.optionalDuration(name, def)
+	if d%time.Millisecond != 0 {
+		r.fail(name, "duration must be a whole number of milliseconds, got %s", d)
+		return 0
+	}
+	return d
+}
+
+func (r *reader) parseDuration(name, v string) time.Duration {
 	d, err := time.ParseDuration(v)
 	if err != nil {
 		r.fail(name, "invalid duration %q (want e.g. 10s, 1m)", v)

internal/config/config_test.go

@@ -3,13 +3,17 @@ package config
 import (
 	"errors"
 	"fmt"
+	"net/netip"
 	"net/url"
 	"os"
 	"path/filepath"
+	"reflect"
 	"slices"
 	"strings"
 	"testing"
 	"time"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/forwarded"
 )
 
 func TestLoad(t *testing.T) {
@@ -21,6 +25,10 @@ func TestLoad(t *testing.T) {
 		t.Fatal(err)
 	}
 	unreadablePath := filepath.Join(dir, "missing_secret")
+	clientSecretPath := filepath.Join(dir, "oidc_client_secret")
+	if err := os.WriteFile(clientSecretPath, []byte("client-s3cret\n"), 0o600); err != nil {
+		t.Fatal(err)
+	}
 	emptyPath := filepath.Join(dir, "empty_secret")
 	if err := os.WriteFile(emptyPath, []byte("\n"), 0o600); err != nil {
 		t.Fatal(err)
@@ -33,6 +41,11 @@ func TestLoad(t *testing.T) {
 			EnvDataDir:         dir,
 			EnvShutdownTimeout: "15s",
 			EnvSecretKeyFile:   secretPath,
+
+			EnvOIDCIssuer:           "https://auth.example.com/application/o/mealquest/",
+			EnvOIDCClientID:         "mealquest",
+			EnvOIDCClientSecretFile: clientSecretPath,
+			EnvOIDCAllowedGroups:    "mealquest-admin",
 		}
 	}
 	with := func(changes map[string]string, unset ...string) map[string]string {
@@ -70,6 +83,7 @@ func TestLoad(t *testing.T) {
 			env:  map[string]string{},
 			badVars: []string{
 				EnvHTTPAddr, EnvPublicURL, EnvDataDir, EnvShutdownTimeout, EnvSecretKeyFile,
+				EnvOIDCIssuer, EnvOIDCClientID, EnvOIDCClientSecretFile, EnvOIDCAllowedGroups,
 			},
 		},
 		{
@@ -139,6 +153,24 @@ func TestLoad(t *testing.T) {
 			env:     with(map[string]string{EnvPublicURL: "http://:8080"}),
 			badVars: []string{EnvPublicURL},
 		},
+		{
+			name:    "plain HTTP public URL on a remote host",
+			env:     with(map[string]string{EnvPublicURL: "http://meals.example.com"}),
+			badVars: []string{EnvPublicURL},
+		},
+		{
+			name:    "plain HTTP public URL on a non-loopback IP",
+			env:     with(map[string]string{EnvPublicURL: "http://192.168.1.20:8080"}),
+			badVars: []string{EnvPublicURL},
+		},
+		{
+			name: "plain HTTP public URL on 127.0.0.1",
+			env:  with(map[string]string{EnvPublicURL: "http://127.0.0.1:8080"}),
+		},
+		{
+			name: "plain HTTP public URL on [::1]",
+			env:  with(map[string]string{EnvPublicURL: "http://[::1]:8080"}),
+		},
 		{
 			name:    "relative public URL",
 			env:     with(map[string]string{EnvPublicURL: "meals.example.com"}),
@@ -169,6 +201,143 @@ func TestLoad(t *testing.T) {
 			env:     with(map[string]string{"MEALQUEST_SECRET_KEY": "inline"}),
 			badVars: []string{"MEALQUEST_SECRET_KEY"},
 		},
+		{
+			name:    "inline OIDC client secret rejected",
+			env:     with(map[string]string{"MEALQUEST_OIDC_CLIENT_SECRET": "inline"}),
+			badVars: []string{"MEALQUEST_OIDC_CLIENT_SECRET"},
+		},
+		{
+			name:    "unreadable OIDC client secret file",
+			env:     with(map[string]string{EnvOIDCClientSecretFile: unreadablePath}),
+			badVars: []string{EnvOIDCClientSecretFile},
+		},
+		{
+			name:    "relative OIDC issuer",
+			env:     with(map[string]string{EnvOIDCIssuer: "auth.example.com"}),
+			badVars: []string{EnvOIDCIssuer},
+		},
+		{
+			name:    "non-http OIDC issuer",
+			env:     with(map[string]string{EnvOIDCIssuer: "ftp://auth.example.com"}),
+			badVars: []string{EnvOIDCIssuer},
+		},
+		{
+			name:    "plain HTTP OIDC issuer on a remote host",
+			env:     with(map[string]string{EnvOIDCIssuer: "http://auth.example.com/application/o/mealquest/"}),
+			badVars: []string{EnvOIDCIssuer},
+		},
+		{
+			name: "plain HTTP OIDC issuer on localhost",
+			env:  with(map[string]string{EnvOIDCIssuer: "http://localhost:9000/application/o/mealquest/"}),
+		},
+		{
+			name: "several allowed groups",
+			env:  with(map[string]string{EnvOIDCAllowedGroups: "mealquest-admin, family"}),
+		},
+		{
+			name:    "empty allowed group entry",
+			env:     with(map[string]string{EnvOIDCAllowedGroups: "mealquest-admin,,family"}),
+			badVars: []string{EnvOIDCAllowedGroups},
+		},
+		{
+			name:    "trailing comma in allowed groups",
+			env:     with(map[string]string{EnvOIDCAllowedGroups: "mealquest-admin,"}),
+			badVars: []string{EnvOIDCAllowedGroups},
+		},
+		{
+			name:    "blank OIDC client ID",
+			env:     with(map[string]string{EnvOIDCClientID: "  "}),
+			badVars: []string{EnvOIDCClientID},
+		},
+		{
+			name: "session lifetimes set",
+			env:  with(map[string]string{EnvSessionIdle: "24h", EnvSessionMax: "48h"}),
+		},
+		{
+			name: "session max equal to idle",
+			env:  with(map[string]string{EnvSessionIdle: "24h", EnvSessionMax: "24h"}),
+		},
+		{
+			name:    "invalid session idle",
+			env:     with(map[string]string{EnvSessionIdle: "a month"}),
+			badVars: []string{EnvSessionIdle},
+		},
+		{
+			name:    "empty session idle",
+			env:     with(map[string]string{EnvSessionIdle: ""}),
+			badVars: []string{EnvSessionIdle},
+		},
+		{
+			name:    "non-positive session max",
+			env:     with(map[string]string{EnvSessionMax: "-1h"}),
+			badVars: []string{EnvSessionMax},
+		},
+		{
+			name: "whole-millisecond session lifetimes",
+			env:  with(map[string]string{EnvSessionIdle: "1ms", EnvSessionMax: "2ms"}),
+		},
+		{
+			name:    "sub-millisecond session idle",
+			env:     with(map[string]string{EnvSessionIdle: "1500us", EnvSessionMax: "2ms"}),
+			badVars: []string{EnvSessionIdle},
+		},
+		{
+			name:    "sub-millisecond session max",
+			env:     with(map[string]string{EnvSessionIdle: "1ms", EnvSessionMax: "1ms500us"}),
+			badVars: []string{EnvSessionMax},
+		},
+		{
+			name:    "session max below idle",
+			env:     with(map[string]string{EnvSessionIdle: "48h", EnvSessionMax: "24h"}),
+			badVars: []string{EnvSessionMax},
+		},
+		{
+			name:    "session max below default idle",
+			env:     with(map[string]string{EnvSessionMax: "719h"}),
+			badVars: []string{EnvSessionMax},
+		},
+		{
+			name: "trusted proxy IP",
+			env:  with(map[string]string{EnvTrustedProxy: "10.60.1.33"}),
+		},
+		{
+			name: "trusted proxy IPs and CIDRs",
+			env:  with(map[string]string{EnvTrustedProxy: "10.60.1.33, 172.16.0.0/12,2001:db8::/32,::1"}),
+		},
+		{
+			name: "blank trusted proxy trusts no peer",
+			env:  with(map[string]string{EnvTrustedProxy: "  "}),
+		},
+		{
+			name:    "trusted proxy not an IP",
+			env:     with(map[string]string{EnvTrustedProxy: "traefik"}),
+			badVars: []string{EnvTrustedProxy},
+		},
+		{
+			name:    "trusted proxy invalid CIDR",
+			env:     with(map[string]string{EnvTrustedProxy: "10.60.1.0/33"}),
+			badVars: []string{EnvTrustedProxy},
+		},
+		{
+			name:    "trusted proxy CIDR with host bits",
+			env:     with(map[string]string{EnvTrustedProxy: "10.60.1.33/24"}),
+			badVars: []string{EnvTrustedProxy},
+		},
+		{
+			name:    "trusted proxy empty entry",
+			env:     with(map[string]string{EnvTrustedProxy: "10.60.1.33,,10.60.1.34"}),
+			badVars: []string{EnvTrustedProxy},
+		},
+		{
+			name:    "trusted proxy trusting everyone",
+			env:     with(map[string]string{EnvTrustedProxy: "0.0.0.0/0"}),
+			badVars: []string{EnvTrustedProxy},
+		},
+		{
+			name:    "trusted proxy with port",
+			env:     with(map[string]string{EnvTrustedProxy: "10.60.1.33:443"}),
+			badVars: []string{EnvTrustedProxy},
+		},
 		{
 			name: "several invalid values are all named",
 			env: with(map[string]string{
@@ -211,7 +380,7 @@ func TestLoad(t *testing.T) {
 					t.Errorf("error message %q does not name %s", err.Error(), v)
 				}
 			}
-			if cfg != (Config{}) {
+			if !reflect.ValueOf(cfg).IsZero() {
 				t.Errorf("load() returned non-zero Config alongside error: %+v", cfg)
 			}
 		})
@@ -226,12 +395,21 @@ func TestLoadValues(t *testing.T) {
 	if err := os.WriteFile(secretPath, []byte("s3cret-value\r\n"), 0o600); err != nil {
 		t.Fatal(err)
 	}
+	clientSecretPath := filepath.Join(dir, "oidc_client_secret")
+	if err := os.WriteFile(clientSecretPath, []byte("client-s3cret\n"), 0o600); err != nil {
+		t.Fatal(err)
+	}
 	env := map[string]string{
 		EnvHTTPAddr:        "127.0.0.1:9000",
 		EnvPublicURL:       "http://localhost:9000",
 		EnvDataDir:         dir,
 		EnvShutdownTimeout: "1m30s",
 		EnvSecretKeyFile:   secretPath,
+
+		EnvOIDCIssuer:           "https://auth.example.com/application/o/mealquest/",
+		EnvOIDCClientID:         "mealquest",
+		EnvOIDCClientSecretFile: clientSecretPath,
+		EnvOIDCAllowedGroups:    " mealquest-admin ,family",
 	}
 	cfg, err := load(func(k string) (string, bool) { v, ok := env[k]; return v, ok })
 	if err != nil {
@@ -253,6 +431,40 @@ func TestLoadValues(t *testing.T) {
 	if cfg.SecretKey.Reveal() != "s3cret-value" {
 		t.Errorf("SecretKey.Reveal() = %q, want trailing newline trimmed", cfg.SecretKey.Reveal())
 	}
+	if got, want := cfg.OIDCIssuer.String(), "https://auth.example.com/application/o/mealquest/"; got != want {
+		t.Errorf("OIDCIssuer = %q, want %q", got, want)
+	}
+	if cfg.OIDCClientID != "mealquest" {
+		t.Errorf("OIDCClientID = %q", cfg.OIDCClientID)
+	}
+	if cfg.OIDCClientSecret.Reveal() != "client-s3cret" {
+		t.Errorf("OIDCClientSecret.Reveal() = %q", cfg.OIDCClientSecret.Reveal())
+	}
+	if want := []string{"mealquest-admin", "family"}; !slices.Equal(cfg.OIDCAllowedGroups, want) {
+		t.Errorf("OIDCAllowedGroups = %q, want %q", cfg.OIDCAllowedGroups, want)
+	}
+	if cfg.SessionIdle != 720*time.Hour || cfg.SessionMax != 4320*time.Hour {
+		t.Errorf("SessionIdle, SessionMax = %v, %v, want defaults 720h, 4320h", cfg.SessionIdle, cfg.SessionMax)
+	}
+
+	if cfg.TrustedProxy != nil {
+		t.Errorf("TrustedProxy = %v, want none when unset", cfg.TrustedProxy)
+	}
+
+	env[EnvSessionIdle] = "12h"
+	env[EnvSessionMax] = "36h"
+	env[EnvTrustedProxy] = "10.60.1.33, 172.16.0.0/12"
+	cfg, err = load(func(k string) (string, bool) { v, ok := env[k]; return v, ok })
+	if err != nil {
+		t.Fatalf("load() error = %v", err)
+	}
+	if cfg.SessionIdle != 12*time.Hour || cfg.SessionMax != 36*time.Hour {
+		t.Errorf("SessionIdle, SessionMax = %v, %v, want 12h, 36h", cfg.SessionIdle, cfg.SessionMax)
+	}
+	want := forwarded.Trusted{netip.MustParsePrefix("10.60.1.33/32"), netip.MustParsePrefix("172.16.0.0/12")}
+	if !slices.Equal(cfg.TrustedProxy, want) {
+		t.Errorf("TrustedProxy = %v, want %v", cfg.TrustedProxy, want)
+	}
 }
 
 func TestSecretRedacted(t *testing.T) {
@@ -260,7 +472,7 @@ func TestSecretRedacted(t *testing.T) {
 
 	s := Secret{value: "s3cret-value"}
 	for _, format := range []string{"%v", "%s", "%+v", "%#v"} {
-		cfg := Config{SecretKey: s}
+		cfg := Config{SecretKey: s, OIDCClientSecret: s}
 		for _, out := range []string{fmt.Sprintf(format, s), fmt.Sprintf(format, cfg)} {
 			if strings.Contains(out, "s3cret-value") {
 				t.Errorf("format %s leaked secret: %s", format, out)

internal/forwarded/forwarded.go

@@ -0,0 +1,221 @@
+// Package forwarded resolves where a request really came from. The service
+// runs behind a reverse proxy (Traefik), so the TCP peer is usually the proxy;
+// the X-Forwarded-For and X-Forwarded-Proto headers it adds are believed only
+// when the peer is a trusted proxy. From anyone else they are ignored, so a
+// client cannot spoof its address or scheme.
+package forwarded
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"log/slog"
+	"net/http"
+	"net/netip"
+	"strings"
+)
+
+// Header names honoured from trusted proxies.
+const (
+	HeaderFor   = "X-Forwarded-For"
+	HeaderProto = "X-Forwarded-Proto"
+)
+
+// ErrInvalidHeader marks a malformed forwarded header from a trusted peer.
+var ErrInvalidHeader = errors.New("invalid forwarded header")
+
+// Trusted is the set of proxy addresses whose forwarded headers are honoured.
+// The zero value trusts no peer.
+type Trusted []netip.Prefix
+
+// ParseTrusted parses a comma-separated list of IP addresses and CIDR
+// prefixes. A blank list trusts no peer. Each entry must be a plain address
+// or a prefix with no host bits set; zones, IPv4-mapped IPv6 forms and
+// zero-length prefixes, which would trust every peer, are rejected.
+func ParseTrusted(s string) (Trusted, error) {
+	if strings.TrimSpace(s) == "" {
+		return nil, nil
+	}
+	var t Trusted
+	for _, entry := range strings.Split(s, ",") {
+		entry = strings.TrimSpace(entry)
+		if entry == "" {
+			return nil, fmt.Errorf("empty entry in comma-separated list %q", s)
+		}
+		p, err := parseEntry(entry)
+		if err != nil {
+			return nil, err
+		}
+		t = append(t, p)
+	}
+	return t, nil
+}
+
+func parseEntry(entry string) (netip.Prefix, error) {
+	var p netip.Prefix
+	if strings.Contains(entry, "/") {
+		var err error
+		p, err = netip.ParsePrefix(entry)
+		if err != nil {
+			return netip.Prefix{}, fmt.Errorf("invalid CIDR %q", entry)
+		}
+		if p != p.Masked() {
+			return netip.Prefix{}, fmt.Errorf("CIDR %q has host bits set (did you mean %s?)", entry, p.Masked())
+		}
+	} else {
+		a, err := netip.ParseAddr(entry)
+		if err != nil {
+			return netip.Prefix{}, fmt.Errorf("invalid IP address %q", entry)
+		}
+		if a.Zone() != "" {
+			return netip.Prefix{}, fmt.Errorf("IP address %q must not have a zone", entry)
+		}
+		p = netip.PrefixFrom(a, a.BitLen())
+	}
+	switch {
+	case p.Addr().Is4In6():
+		return netip.Prefix{}, fmt.Errorf("%q is IPv4-mapped IPv6; write the IPv4 form", entry)
+	case p.Bits() == 0:
+		return netip.Prefix{}, fmt.Errorf("%q would trust every peer", entry)
+	}
+	return p, nil
+}
+
+// Contains reports whether a is a trusted proxy address. IPv4-mapped IPv6
+// addresses, as a dual-stack listener reports IPv4 peers, match their IPv4
+// form.
+func (t Trusted) Contains(a netip.Addr) bool {
+	a = normalize(a)
+	for _, p := range t {
+		if p.Contains(a) {
+			return true
+		}
+	}
+	return false
+}
+
+func normalize(a netip.Addr) netip.Addr { return a.Unmap().WithZone("") }
+
+// Origin is where a request came from.
+type Origin struct {
+	// ClientIP is the client's address.
+	ClientIP netip.Addr
+	// Scheme is "https" or "http": the scheme the client used.
+	Scheme string
+}
+
+// Resolve works out r's Origin. When the TCP peer (r.RemoteAddr) is not in
+// trusted, both forwarded headers are ignored: the client is the peer and the
+// scheme is that of the connection.
+//
+// When the peer is trusted:
+//   - X-Forwarded-For entries (across all its header lines, in order) are
+//     walked right to left, skipping trusted proxy addresses; the first
+//     untrusted address is the client. Entries left of it are client-supplied
+//     and not examined. If every entry is trusted the leftmost is the client;
+//     with no X-Forwarded-For the peer is the client.
+//   - X-Forwarded-Proto, if present, must be a single "http" or "https" and
+//     is the scheme; without it the connection's scheme is used.
+//
+// A malformed header from a trusted peer is an error wrapping
+// ErrInvalidHeader; any other error means RemoteAddr is not an IP and port.
+func Resolve(r *http.Request, trusted Trusted) (Origin, error) {
+	peer, err := netip.ParseAddrPort(r.RemoteAddr)
+	if err != nil {
+		return Origin{}, fmt.Errorf("peer address %q is not an IP and port", r.RemoteAddr)
+	}
+	o := Origin{ClientIP: normalize(peer.Addr()), Scheme: "http"}
+	if r.TLS != nil {
+		o.Scheme = "https"
+	}
+	if !trusted.Contains(o.ClientIP) {
+		return o, nil
+	}
+	if values := r.Header.Values(HeaderFor); len(values) > 0 {
+		o.ClientIP, err = clientFromChain(strings.Split(strings.Join(values, ","), ","), trusted)
+		if err != nil {
+			return Origin{}, err
+		}
+	}
+	switch values := r.Header.Values(HeaderProto); len(values) {
+	case 0:
+	case 1:
+		switch scheme := strings.ToLower(strings.TrimSpace(values[0])); scheme {
+		case "http", "https":
+			o.Scheme = scheme
+		default:
+			return Origin{}, fmt.Errorf("%w: %s %q is not http or https", ErrInvalidHeader, HeaderProto, values[0])
+		}
+	default:
+		return Origin{}, fmt.Errorf("%w: %d %s headers, want one", ErrInvalidHeader, len(values), HeaderProto)
+	}
+	return o, nil
+}
+
+// clientFromChain returns the rightmost untrusted address in chain, or the
+// leftmost address when all are trusted.
+func clientFromChain(chain []string, trusted Trusted) (netip.Addr, error) {
+	var client netip.Addr
+	for i := len(chain) - 1; i >= 0; i-- {
+		a, err := netip.ParseAddr(strings.TrimSpace(chain[i]))
+		if err != nil {
+			return netip.Addr{}, fmt.Errorf("%w: %s entry %q is not an IP address", ErrInvalidHeader, HeaderFor, strings.TrimSpace(chain[i]))
+		}
+		client = normalize(a)
+		if !trusted.Contains(client) {
+			break
+		}
+	}
+	return client, nil
+}
+
+type contextKey struct{}
+
+// NewContext returns ctx carrying o.
+func NewContext(ctx context.Context, o Origin) context.Context {
+	return context.WithValue(ctx, contextKey{}, o)
+}
+
+// FromContext returns the Origin ctx carries; ok is false when the request
+// was not resolved.
+func FromContext(ctx context.Context) (o Origin, ok bool) {
+	o, ok = ctx.Value(contextKey{}).(Origin)
+	return o, ok
+}
+
+// ClientIP returns the resolved client address ctx carries.
+func ClientIP(ctx context.Context) (netip.Addr, bool) {
+	o, ok := FromContext(ctx)
+	return o.ClientIP, ok
+}
+
+// Scheme returns the resolved request scheme ctx carries.
+func Scheme(ctx context.Context) (string, bool) {
+	o, ok := FromContext(ctx)
+	return o.Scheme, ok
+}
+
+// LogAttr is the log attribute key for the resolved client address.
+const LogAttr = "client_ip"
+
+// LogHandler wraps h so every record logged with a resolved request's
+// context carries the client address as LogAttr.
+func LogHandler(h slog.Handler) slog.Handler { return logHandler{h} }
+
+type logHandler struct{ slog.Handler }
+
+func (h logHandler) Handle(ctx context.Context, rec slog.Record) error {
+	if ip, ok := ClientIP(ctx); ok {
+		rec = rec.Clone()
+		rec.AddAttrs(slog.String(LogAttr, ip.String()))
+	}
+	return h.Handler.Handle(ctx, rec)
+}
+
+func (h logHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
+	return logHandler{h.Handler.WithAttrs(attrs)}
+}
+
+func (h logHandler) WithGroup(name string) slog.Handler {
+	return logHandler{h.Handler.WithGroup(name)}
+}

internal/forwarded/forwarded_test.go

@@ -0,0 +1,260 @@
+package forwarded
+
+import (
+	"bytes"
+	"context"
+	"crypto/tls"
+	"errors"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"net/netip"
+	"slices"
+	"strings"
+	"testing"
+)
+
+func TestParseTrusted(t *testing.T) {
+	t.Parallel()
+	tests := []struct {
+		in      string
+		want    []string
+		wantErr string
+	}{
+		{in: "", want: nil},
+		{in: "   ", want: nil},
+		{in: "10.60.1.33", want: []string{"10.60.1.33/32"}},
+		{in: "10.60.1.33, 172.16.0.0/12", want: []string{"10.60.1.33/32", "172.16.0.0/12"}},
+		{in: "2001:db8::1,2001:db8::/32", want: []string{"2001:db8::1/128", "2001:db8::/32"}},
+		{in: "traefik", wantErr: "invalid IP address"},
+		{in: "10.60.1.33:443", wantErr: "invalid IP address"},
+		{in: "10.60.1.0/33", wantErr: "invalid CIDR"},
+		{in: "10.60.1.33/24", wantErr: "did you mean 10.60.1.0/24"},
+		{in: "10.60.1.33,,10.60.1.34", wantErr: "empty entry"},
+		{in: "10.60.1.33,", wantErr: "empty entry"},
+		{in: "fe80::1%eth0", wantErr: "zone"},
+		{in: "::ffff:10.60.1.33", wantErr: "IPv4-mapped"},
+		{in: "0.0.0.0/0", wantErr: "every peer"},
+		{in: "::/0", wantErr: "every peer"},
+	}
+	for _, tt := range tests {
+		got, err := ParseTrusted(tt.in)
+		if tt.wantErr != "" {
+			if err == nil || !strings.Contains(err.Error(), tt.wantErr) {
+				t.Errorf("ParseTrusted(%q) error = %v, want one containing %q", tt.in, err, tt.wantErr)
+			}
+			continue
+		}
+		if err != nil {
+			t.Errorf("ParseTrusted(%q) error = %v", tt.in, err)
+			continue
+		}
+		var gotStr []string
+		for _, p := range got {
+			gotStr = append(gotStr, p.String())
+		}
+		if !slices.Equal(gotStr, tt.want) {
+			t.Errorf("ParseTrusted(%q) = %v, want %v", tt.in, gotStr, tt.want)
+		}
+	}
+}
+
+func TestTrustedContainsMappedIPv4(t *testing.T) {
+	t.Parallel()
+	trusted := mustTrusted(t, "10.60.1.33")
+	if !trusted.Contains(netip.MustParseAddr("::ffff:10.60.1.33")) {
+		t.Error("IPv4-mapped form of a trusted address is not trusted")
+	}
+	if Trusted(nil).Contains(netip.MustParseAddr("10.60.1.33")) {
+		t.Error("an empty set trusts a peer")
+	}
+}
+
+func mustTrusted(t *testing.T, s string) Trusted {
+	t.Helper()
+	tr, err := ParseTrusted(s)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return tr
+}
+
+func TestResolve(t *testing.T) {
+	t.Parallel()
+	// 10.60.1.33 is Traefik; 10.60.2.0/24 is an inner proxy tier.
+	trusted := mustTrusted(t, "10.60.1.33,10.60.2.0/24")
+	tests := []struct {
+		name       string
+		peer       string
+		tls        bool
+		xff        []string
+		xfp        []string
+		wantIP     string
+		wantScheme string
+	}{
+		{
+			name: "untrusted peer, no headers",
+			peer: "198.51.100.9:5000", wantIP: "198.51.100.9", wantScheme: "http",
+		},
+		{
+			name: "untrusted peer over TLS",
+			peer: "198.51.100.9:5000", tls: true, wantIP: "198.51.100.9", wantScheme: "https",
+		},
+		{
+			name: "untrusted peer spoofing both headers is ignored",
+			peer: "198.51.100.9:5000", xff: []string{"203.0.113.7"}, xfp: []string{"https"},
+			wantIP: "198.51.100.9", wantScheme: "http",
+		},
+		{
+			name: "untrusted peer's malformed headers are ignored, not rejected",
+			peer: "198.51.100.9:5000", xff: []string{"not-an-ip"}, xfp: []string{"gopher"},
+			wantIP: "198.51.100.9", wantScheme: "http",
+		},
+		{
+			name: "trusted peer: client from X-Forwarded-For, scheme from X-Forwarded-Proto",
+			peer: "10.60.1.33:41000", xff: []string{"203.0.113.7"}, xfp: []string{"https"},
+			wantIP: "203.0.113.7", wantScheme: "https",
+		},
+		{
+			name: "trusted peer seen as IPv4-mapped IPv6",
+			peer: "[::ffff:10.60.1.33]:41000", xff: []string{"203.0.113.7"}, xfp: []string{"https"},
+			wantIP: "203.0.113.7", wantScheme: "https",
+		},
+		{
+			name: "trusted peer without headers is itself the client",
+			peer: "10.60.1.33:41000", wantIP: "10.60.1.33", wantScheme: "http",
+		},
+		{
+			name: "rightmost untrusted address wins over a client-supplied prefix",
+			peer: "10.60.1.33:41000", xff: []string{"1.2.3.4, 203.0.113.7"}, xfp: []string{"https"},
+			wantIP: "203.0.113.7", wantScheme: "https",
+		},
+		{
+			name: "trusted proxies in the chain are skipped",
+			peer: "10.60.1.33:41000", xff: []string{"1.2.3.4, 203.0.113.7, 10.60.2.5"}, xfp: []string{"https"},
+			wantIP: "203.0.113.7", wantScheme: "https",
+		},
+		{
+			name: "several header lines form one chain",
+			peer: "10.60.1.33:41000", xff: []string{"1.2.3.4", "203.0.113.7, 10.60.2.5"},
+			wantIP: "203.0.113.7", wantScheme: "http",
+		},
+		{
+			name: "garbage left of the client is not examined",
+			peer: "10.60.1.33:41000", xff: []string{"spoofed, 203.0.113.7"},
+			wantIP: "203.0.113.7", wantScheme: "http",
+		},
+		{
+			name: "all trusted: leftmost is the client",
+			peer: "10.60.1.33:41000", xff: []string{"10.60.2.5, 10.60.2.6"},
+			wantIP: "10.60.2.5", wantScheme: "http",
+		},
+		{
+			name: "IPv6 client",
+			peer: "10.60.1.33:41000", xff: []string{"2001:db8::7"}, xfp: []string{"HTTPS"},
+			wantIP: "2001:db8::7", wantScheme: "https",
+		},
+		{
+			name: "trusted peer may downgrade to http",
+			peer: "10.60.1.33:41000", tls: true, xfp: []string{"http"},
+			wantIP: "10.60.1.33", wantScheme: "http",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			r := request(tt.peer, tt.xff, tt.xfp)
+			if tt.tls {
+				r.TLS = &tls.ConnectionState{}
+			}
+			o, err := Resolve(r, trusted)
+			if err != nil {
+				t.Fatalf("Resolve error = %v", err)
+			}
+			if o.ClientIP.String() != tt.wantIP || o.Scheme != tt.wantScheme {
+				t.Errorf("Resolve = %s %s, want %s %s", o.ClientIP, o.Scheme, tt.wantIP, tt.wantScheme)
+			}
+		})
+	}
+}
+
+func TestResolveRejectsMalformedHeadersFromTrustedPeer(t *testing.T) {
+	t.Parallel()
+	trusted := mustTrusted(t, "10.60.1.33")
+	for _, tt := range []struct {
+		name     string
+		xff, xfp []string
+	}{
+		{"X-Forwarded-For not an IP", []string{"not-an-ip"}, nil},
+		{"X-Forwarded-For with a port", []string{"203.0.113.7:5000"}, nil},
+		{"X-Forwarded-For empty entry", []string{"203.0.113.7, "}, nil},
+		{"X-Forwarded-For empty", []string{""}, nil},
+		{"X-Forwarded-Proto unknown scheme", nil, []string{"ftp"}},
+		{"X-Forwarded-Proto list", nil, []string{"https, http"}},
+		{"X-Forwarded-Proto repeated", nil, []string{"https", "https"}},
+	} {
+		_, err := Resolve(request("10.60.1.33:41000", tt.xff, tt.xfp), trusted)
+		if !errors.Is(err, ErrInvalidHeader) {
+			t.Errorf("%s: Resolve error = %v, want ErrInvalidHeader", tt.name, err)
+		}
+	}
+}
+
+func TestResolveBadPeerAddress(t *testing.T) {
+	t.Parallel()
+	r := request("@", nil, nil)
+	_, err := Resolve(r, nil)
+	if err == nil || errors.Is(err, ErrInvalidHeader) {
+		t.Errorf("Resolve error = %v, want a peer address error", err)
+	}
+}
+
+func request(peer string, xff, xfp []string) *http.Request {
+	r := httptest.NewRequest(http.MethodGet, "/", nil)
+	r.RemoteAddr = peer
+	for _, v := range xff {
+		r.Header.Add(HeaderFor, v)
+	}
+	for _, v := range xfp {
+		r.Header.Add(HeaderProto, v)
+	}
+	return r
+}
+
+func TestContextHelpers(t *testing.T) {
+	t.Parallel()
+	if _, ok := ClientIP(context.Background()); ok {
+		t.Error("ClientIP ok on an unresolved context")
+	}
+	if _, ok := Scheme(context.Background()); ok {
+		t.Error("Scheme ok on an unresolved context")
+	}
+	ctx := NewContext(context.Background(), Origin{ClientIP: netip.MustParseAddr("203.0.113.7"), Scheme: "https"})
+	if ip, ok := ClientIP(ctx); !ok || ip.String() != "203.0.113.7" {
+		t.Errorf("ClientIP = %s %v, want 203.0.113.7 true", ip, ok)
+	}
+	if s, ok := Scheme(ctx); !ok || s != "https" {
+		t.Errorf("Scheme = %q %v, want https true", s, ok)
+	}
+}
+
+func TestLogHandler(t *testing.T) {
+	t.Parallel()
+	var buf bytes.Buffer
+	logger := slog.New(LogHandler(slog.NewTextHandler(&buf, nil))).With("component", "test")
+	ctx := NewContext(context.Background(), Origin{ClientIP: netip.MustParseAddr("203.0.113.7"), Scheme: "https"})
+
+	logger.InfoContext(ctx, "resolved")
+	logger.InfoContext(context.Background(), "unresolved")
+
+	lines := strings.Split(strings.TrimSpace(buf.String()), "\n")
+	if len(lines) != 2 {
+		t.Fatalf("logged %d lines, want 2: %q", len(lines), buf.String())
+	}
+	if !strings.Contains(lines[0], "client_ip=203.0.113.7") || !strings.Contains(lines[0], "component=test") {
+		t.Errorf("resolved line = %q, want client_ip and the With attribute", lines[0])
+	}
+	if strings.Contains(lines[1], "client_ip") {
+		t.Errorf("unresolved line = %q, want no client_ip", lines[1])
+	}
+}

internal/secureurl/secureurl.go

@@ -0,0 +1,32 @@
+// Package secureurl holds the one transport rule for URLs that carry
+// credentials or session cookies: HTTPS, or plain HTTP to a loopback host for
+// local development and tests.
+package secureurl
+
+import (
+	"errors"
+	"fmt"
+	"net/url"
+	"strings"
+)
+
+// loopbackHosts are the only hosts plain HTTP is allowed for, compared
+// case-insensitively. url.URL's Hostname strips the brackets from "[::1]".
+var loopbackHosts = map[string]bool{"localhost": true, "127.0.0.1": true, "::1": true}
+
+// Check reports an error unless u is an absolute https:// URL, or an http://
+// URL whose host is localhost, 127.0.0.1 or ::1.
+func Check(u *url.URL) error {
+	switch {
+	case u.Hostname() == "":
+		return errors.New("URL has no host")
+	case u.Scheme == "https":
+		return nil
+	case u.Scheme == "http" && loopbackHosts[strings.ToLower(u.Hostname())]:
+		return nil
+	case u.Scheme == "http":
+		return errors.New("plain http:// is allowed only for localhost, 127.0.0.1 or [::1]; use https://")
+	default:
+		return fmt.Errorf("unsupported scheme %q (want https://)", u.Scheme)
+	}
+}

internal/secureurl/secureurl_test.go

@@ -0,0 +1,40 @@
+package secureurl
+
+import (
+	"net/url"
+	"testing"
+)
+
+func TestCheck(t *testing.T) {
+	t.Parallel()
+	tests := []struct {
+		raw string
+		ok  bool
+	}{
+		{"https://meals.example.com", true},
+		{"https://auth.example.com/application/o/mealquest/", true},
+		{"https://192.0.2.10:8443", true},
+		{"http://localhost:8080", true},
+		{"http://LOCALHOST:8080", true},
+		{"http://127.0.0.1:8080/path", true},
+		{"http://[::1]:8080", true},
+		{"http://[::1]", true},
+		{"http://meals.example.com", false},
+		{"http://192.0.2.10", false},
+		{"http://127.0.0.2", false},
+		{"http://localhost.example.com", false},
+		{"http://0.0.0.0:8080", false},
+		{"ftp://localhost", false},
+		{"https://", false},
+		{"meals.example.com", false},
+	}
+	for _, tc := range tests {
+		u, err := url.Parse(tc.raw)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if err := Check(u); (err == nil) != tc.ok {
+			t.Errorf("Check(%q) error = %v, want ok=%v", tc.raw, err, tc.ok)
+		}
+	}
+}

internal/server/csrf.go

@@ -0,0 +1,42 @@
+package server
+
+import (
+	"crypto/subtle"
+	"log/slog"
+	"net/http"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/auth"
+)
+
+// CSRFHeader carries the session's CSRF token, which the client reads from
+// GET /api/v1/me.
+const CSRFHeader = "X-MealQuest-CSRF"
+
+// requireCSRF passes GET requests to next; every other
+// request must carry CSRFHeader equal to its session's CSRF token or get 403
+// csrf. It runs behind requireSession, which puts the session in the context.
+func requireCSRF(logger *slog.Logger) func(http.Handler) http.Handler {
+	forbidden := apiErrorHandler(logger, http.StatusForbidden, "csrf", "missing or invalid CSRF token")
+	internal := apiErrorHandler(logger, http.StatusInternalServerError, "internal", "internal error")
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			switch r.Method {
+			case http.MethodGet:
+				next.ServeHTTP(w, r)
+				return
+			}
+			s, ok := auth.SessionFrom(r.Context())
+			if !ok || s.CSRFToken == "" {
+				// An empty token would match a missing header.
+				logger.ErrorContext(r.Context(), "csrf check without a session token", "session", ok)
+				internal(w, r)
+				return
+			}
+			if subtle.ConstantTimeCompare([]byte(r.Header.Get(CSRFHeader)), []byte(s.CSRFToken)) != 1 {
+				forbidden(w, r)
+				return
+			}
+			next.ServeHTTP(w, r)
+		})
+	}
+}

internal/server/csrf_test.go

@@ -0,0 +1,166 @@
+package server
+
+import (
+	"context"
+	"encoding/json"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/auth"
+)
+
+const (
+	csrfJSON             = `{"error":{"code":"csrf","message":"missing or invalid CSRF token","retryable":false}}`
+	methodNotAllowedJSON = `{"error":{"code":"method_not_allowed","message":"method not allowed","retryable":false}}`
+)
+
+func TestCSRFThroughRouter(t *testing.T) {
+	t.Parallel()
+
+	router := newTestRouter(t, "dev")
+	for _, tc := range []struct {
+		name, method, path string
+		header             []string // nil sends no CSRF header
+		wantStatus         int
+		wantBody           string
+	}{
+		{"POST without header", http.MethodPost, "/api/v1/me", nil, http.StatusForbidden, csrfJSON},
+		{"POST with wrong header", http.MethodPost, "/api/v1/me", []string{"wrong-token"}, http.StatusForbidden, csrfJSON},
+		{"POST with empty header", http.MethodPost, "/api/v1/me", []string{""}, http.StatusForbidden, csrfJSON},
+		{"POST with token prefix", http.MethodPost, "/api/v1/me", []string{"csrf-token"}, http.StatusForbidden, csrfJSON},
+		{"PATCH without header", http.MethodPatch, "/api/v1/settings/household", nil, http.StatusForbidden, csrfJSON},
+		{"DELETE with wrong header", http.MethodDelete, "/api/v1/me", []string{"wrong-token"}, http.StatusForbidden, csrfJSON},
+		// The right token passes the check and reaches the router, which has
+		// no POST /api/v1/me.
+		{"POST with right header", http.MethodPost, "/api/v1/me", []string{testSession.CSRFToken}, http.StatusMethodNotAllowed, methodNotAllowedJSON},
+		{"PATCH with right header", http.MethodPatch, "/api/v1/settings/household", []string{testSession.CSRFToken}, http.StatusNotFound, notFoundJSON},
+		{"GET without header", http.MethodGet, "/api/v1/me", nil, http.StatusOK, ""},
+		// Only GET is exempt; HEAD and OPTIONS need the header too.
+		{"HEAD without header", http.MethodHead, "/api/v1/me", nil, http.StatusForbidden, csrfJSON},
+		{"OPTIONS without header", http.MethodOptions, "/api/v1/me", nil, http.StatusForbidden, csrfJSON},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			req := httptest.NewRequest(tc.method, tc.path, nil)
+			req.AddCookie(validSessionCookie)
+			if tc.header != nil {
+				req.Header.Set(CSRFHeader, tc.header[0])
+			}
+			rec := httptest.NewRecorder()
+			router.ServeHTTP(rec, req)
+
+			if rec.Code != tc.wantStatus {
+				t.Errorf("status = %d, want %d (body %s)", rec.Code, tc.wantStatus, rec.Body.String())
+			}
+			if tc.wantBody != "" && rec.Body.String() != tc.wantBody {
+				t.Errorf("body = %s, want %s", rec.Body.String(), tc.wantBody)
+			}
+		})
+	}
+}
+
+func TestCSRFUnauthenticatedGets401(t *testing.T) {
+	t.Parallel()
+
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/me", nil)
+	rec := httptest.NewRecorder()
+	newTestRouter(t, "dev").ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusUnauthorized || rec.Body.String() != unauthenticatedJSON {
+		t.Errorf("response = %d %s, want 401 %s", rec.Code, rec.Body.String(), unauthenticatedJSON)
+	}
+}
+
+func TestRequireCSRF(t *testing.T) {
+	t.Parallel()
+
+	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
+	for _, tc := range []struct {
+		name       string
+		method     string
+		session    *auth.Session
+		header     string
+		wantStatus int
+	}{
+		{"right header reaches handler", http.MethodPost, &testSession, testSession.CSRFToken, http.StatusNoContent},
+		{"wrong header", http.MethodPut, &testSession, "nope", http.StatusForbidden},
+		{"GET needs no header", http.MethodGet, &testSession, "", http.StatusNoContent},
+		{"HEAD needs the header", http.MethodHead, &testSession, "", http.StatusForbidden},
+		{"OPTIONS needs the header", http.MethodOptions, &testSession, "", http.StatusForbidden},
+		{"no session in context", http.MethodPost, nil, "", http.StatusInternalServerError},
+		{"session without token", http.MethodPost, &auth.Session{Subject: "user-123"}, "", http.StatusInternalServerError},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			called := false
+			h := requireCSRF(logger)(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+				called = true
+				w.WriteHeader(http.StatusNoContent)
+			}))
+			ctx := context.Background()
+			if tc.session != nil {
+				ctx = auth.WithSession(ctx, *tc.session)
+			}
+			req := httptest.NewRequestWithContext(ctx, tc.method, "/api/v1/anything", nil)
+			if tc.header != "" {
+				req.Header.Set(CSRFHeader, tc.header)
+			}
+			rec := httptest.NewRecorder()
+			h.ServeHTTP(rec, req)
+
+			if rec.Code != tc.wantStatus {
+				t.Errorf("status = %d, want %d", rec.Code, tc.wantStatus)
+			}
+			if called != (tc.wantStatus == http.StatusNoContent) {
+				t.Errorf("handler called = %v with status %d", called, rec.Code)
+			}
+		})
+	}
+}
+
+func TestMe(t *testing.T) {
+	t.Parallel()
+
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/me", nil)
+	req.AddCookie(validSessionCookie)
+	rec := httptest.NewRecorder()
+	newTestRouter(t, "dev").ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200 (body %s)", rec.Code, rec.Body.String())
+	}
+	if ct := rec.Header().Get("Content-Type"); ct != "application/json" {
+		t.Errorf("Content-Type = %q, want application/json", ct)
+	}
+	if cc := rec.Header().Get("Cache-Control"); cc != "no-store" {
+		t.Errorf("Cache-Control = %q, want no-store", cc)
+	}
+	var got map[string]any
+	if err := json.Unmarshal(rec.Body.Bytes(), &got); err != nil {
+		t.Fatalf("decode %s: %v", rec.Body.String(), err)
+	}
+	want := map[string]any{
+		"name":      "Home Cook",
+		"email":     "cook@example.com",
+		"household": map[string]any{"label": "Our kitchen"},
+		"csrfToken": "csrf-token-123",
+	}
+	gotJSON, _ := json.Marshal(got)
+	wantJSON, _ := json.Marshal(want)
+	if string(gotJSON) != string(wantJSON) {
+		t.Errorf("body = %s, want %s", gotJSON, wantJSON)
+	}
+}
+
+func TestMeNeedsSession(t *testing.T) {
+	t.Parallel()
+
+	rec := httptest.NewRecorder()
+	newTestRouter(t, "dev").ServeHTTP(rec, httptest.NewRequest(http.MethodGet, "/api/v1/me", nil))
+	if rec.Code != http.StatusUnauthorized || rec.Body.String() != unauthenticatedJSON {
+		t.Errorf("response = %d %s, want 401 %s", rec.Code, rec.Body.String(), unauthenticatedJSON)
+	}
+}

internal/server/login_test.go

@@ -0,0 +1,140 @@
+package server
+
+import (
+	"context"
+	"encoding/json"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+	"testing/fstest"
+	"time"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/auth"
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/forwarded"
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/store"
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/migrations"
+)
+
+// newDiscoveryProvider serves the OIDC discovery document auth.New needs;
+// login only redirects to its authorization endpoint.
+func newDiscoveryProvider(t *testing.T) *httptest.Server {
+	t.Helper()
+	var srv *httptest.Server
+	srv = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/.well-known/openid-configuration" {
+			http.NotFound(w, r)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(map[string]any{
+			"issuer":                                srv.URL,
+			"authorization_endpoint":                srv.URL + "/authorize",
+			"token_endpoint":                        srv.URL + "/token",
+			"jwks_uri":                              srv.URL + "/jwks",
+			"userinfo_endpoint":                     srv.URL + "/userinfo",
+			"end_session_endpoint":                  srv.URL + "/end-session/",
+			"response_types_supported":              []string{"code"},
+			"subject_types_supported":               []string{"public"},
+			"id_token_signing_alg_values_supported": []string{"RS256"},
+		})
+	}))
+	t.Cleanup(srv.Close)
+	return srv
+}
+
+// newLoginRouter wires the production router as cmd/server does: the real
+// auth flow and session manager, trusting Traefik only.
+func newLoginRouter(t *testing.T, issuer string) http.Handler {
+	t.Helper()
+	ctx := context.Background()
+	db, err := store.Open(ctx, t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := db.Close(); err != nil {
+			t.Error(err)
+		}
+	})
+	if err := store.Migrate(ctx, db.Writer, migrations.FS); err != nil {
+		t.Fatal(err)
+	}
+	sessions, err := auth.NewSessionManager(db, 720*time.Hour, 4320*time.Hour)
+	if err != nil {
+		t.Fatal(err)
+	}
+	logger := slog.New(forwarded.LogHandler(slog.NewTextHandler(io.Discard, nil)))
+	flow, err := auth.New(ctx, auth.Config{
+		Issuer:        issuer,
+		ClientID:      "mealquest",
+		ClientSecret:  "client-s3cret",
+		PublicURL:     &url.URL{Scheme: "https", Host: "meals.example.com"},
+		SecretKey:     []byte("server-secret-key"),
+		AllowedGroups: []string{"mealquest-admin"},
+	}, sessions, logger)
+	if err != nil {
+		t.Fatal(err)
+	}
+	trusted, err := forwarded.ParseTrusted(traefik)
+	if err != nil {
+		t.Fatal(err)
+	}
+	r, err := NewRouter(logger, "dev", trusted, flow, sessions,
+		fstest.MapFS{"index.html": {Data: []byte(fixtureIndex)}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	return r
+}
+
+// TestLoginThroughRouter starts a login through the production router. The
+// redirect URI and the Secure login cookie come from MEALQUEST_PUBLIC_URL
+// whatever the direct peer: forwarded headers from an untrusted peer are
+// ignored but never fail sign-in.
+func TestLoginThroughRouter(t *testing.T) {
+	t.Parallel()
+	provider := newDiscoveryProvider(t)
+	router := newLoginRouter(t, provider.URL)
+	// Traefik reaches the service over plain http on its internal address;
+	// the host headers must not leak into the redirect URI.
+	headers := map[string]string{
+		forwarded.HeaderFor:   "203.0.113.7",
+		forwarded.HeaderProto: "https",
+		"X-Forwarded-Host":    "evil.example.com",
+	}
+	tests := []struct {
+		name string
+		peer string
+	}{
+		{"trusted proxy", traefik + ":41000"},
+		{"untrusted peer", "172.17.0.1:5000"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			rec := httptest.NewRecorder()
+			router.ServeHTTP(rec, originRequest("http://mealquest:8080"+auth.LoginPath, tt.peer, headers))
+			resp := rec.Result()
+			if resp.StatusCode != http.StatusFound {
+				t.Fatalf("login status = %d, want 302", resp.StatusCode)
+			}
+			loc, err := url.Parse(resp.Header.Get("Location"))
+			if err != nil {
+				t.Fatal(err)
+			}
+			if got, want := loc.Scheme+"://"+loc.Host+loc.Path, provider.URL+"/authorize"; got != want {
+				t.Errorf("redirect to %s, want %s", got, want)
+			}
+			if got, want := loc.Query().Get("redirect_uri"), "https://meals.example.com/auth/callback"; got != want {
+				t.Errorf("redirect_uri = %q, want %q from the public URL", got, want)
+			}
+			cookies := resp.Cookies()
+			if len(cookies) != 1 || cookies[0].Name != "__Host-mealquest_login" || !cookies[0].Secure || !cookies[0].HttpOnly {
+				t.Errorf("login cookies = %v, want one Secure, HttpOnly __Host-mealquest_login", cookies)
+			}
+		})
+	}
+}

internal/server/me.go

@@ -0,0 +1,52 @@
+package server
+
+import (
+	"encoding/json"
+	"log/slog"
+	"net/http"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/auth"
+)
+
+// householdLabel is the single shared household identity.
+const householdLabel = "Our kitchen"
+
+type meResponse struct {
+	Name      string        `json:"name"`
+	Email     string        `json:"email"`
+	Household householdInfo `json:"household"`
+	CSRFToken string        `json:"csrfToken"`
+}
+
+type householdInfo struct {
+	Label string `json:"label"`
+}
+
+// me answers GET /api/v1/me with the signed-in member, the household and the
+// session's CSRF token for CSRFHeader.
+func me(logger *slog.Logger) http.HandlerFunc {
+	internal := apiErrorHandler(logger, http.StatusInternalServerError, "internal", "internal error")
+	return func(w http.ResponseWriter, r *http.Request) {
+		s, ok := auth.SessionFrom(r.Context())
+		if !ok {
+			logger.ErrorContext(r.Context(), "GET /api/v1/me without a session")
+			internal(w, r)
+			return
+		}
+		body, err := json.Marshal(meResponse{
+			Name:      s.Name,
+			Email:     s.Email,
+			Household: householdInfo{Label: householdLabel},
+			CSRFToken: s.CSRFToken,
+		})
+		if err != nil {
+			panic(err) // string fields cannot fail to marshal
+		}
+		w.Header().Set("Content-Type", "application/json")
+		w.Header().Set("Cache-Control", "no-store")
+		w.WriteHeader(http.StatusOK)
+		if _, err := w.Write(body); err != nil {
+			logger.WarnContext(r.Context(), "write me response", "error", err)
+		}
+	}
+}

internal/server/origin.go

@@ -0,0 +1,34 @@
+package server
+
+import (
+	"errors"
+	"log/slog"
+	"net/http"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/forwarded"
+)
+
+// resolveOrigin resolves every request's client address and scheme with
+// forwarded.Resolve and puts them in the context (read them with
+// forwarded.ClientIP and forwarded.Scheme). Forwarded headers are honoured
+// only from a peer in trusted. A malformed forwarded header from a trusted
+// peer gets 400 bad_request.
+func resolveOrigin(logger *slog.Logger, trusted forwarded.Trusted) func(http.Handler) http.Handler {
+	badRequest := apiErrorHandler(logger, http.StatusBadRequest, "bad_request", "invalid forwarded headers")
+	internal := apiErrorHandler(logger, http.StatusInternalServerError, "internal", "internal error")
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			o, err := forwarded.Resolve(r, trusted)
+			switch {
+			case errors.Is(err, forwarded.ErrInvalidHeader):
+				logger.WarnContext(r.Context(), "rejected forwarded headers", "peer", r.RemoteAddr, "error", err)
+				badRequest(w, r)
+			case err != nil:
+				logger.ErrorContext(r.Context(), "resolve request origin", "error", err)
+				internal(w, r)
+			default:
+				next.ServeHTTP(w, r.WithContext(forwarded.NewContext(r.Context(), o)))
+			}
+		})
+	}
+}

internal/server/origin_test.go

@@ -0,0 +1,145 @@
+package server
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"testing/fstest"
+
+	"github.com/go-chi/chi/v5"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/forwarded"
+)
+
+// traefik is the production proxy's address.
+const traefik = "10.60.1.33"
+
+// probeAuth mounts GET /auth/probe, which reports the request's resolved
+// origin, in place of the real auth flow.
+type probeAuth struct{}
+
+func (probeAuth) Mount(r chi.Router) {
+	r.Get("/auth/probe", func(w http.ResponseWriter, r *http.Request) {
+		ip, ipOK := forwarded.ClientIP(r.Context())
+		scheme, schemeOK := forwarded.Scheme(r.Context())
+		if !ipOK || !schemeOK {
+			http.Error(w, "origin not resolved", http.StatusInternalServerError)
+			return
+		}
+		fmt.Fprintf(w, "%s %s", ip, scheme)
+	})
+}
+
+// newOriginRouter builds the production router trusting Traefik, logging
+// through forwarded.LogHandler as cmd/server does.
+func newOriginRouter(t *testing.T, logs io.Writer) http.Handler {
+	t.Helper()
+	trusted, err := forwarded.ParseTrusted(traefik)
+	if err != nil {
+		t.Fatal(err)
+	}
+	logger := slog.New(forwarded.LogHandler(slog.NewJSONHandler(logs, nil)))
+	r, err := NewRouter(logger, "dev", trusted, probeAuth{}, stubSessions{},
+		fstest.MapFS{"index.html": {Data: []byte(fixtureIndex)}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	return r
+}
+
+func originRequest(target, peer string, headers map[string]string) *http.Request {
+	req := httptest.NewRequest(http.MethodGet, target, nil)
+	req.RemoteAddr = peer
+	for k, v := range headers {
+		req.Header.Set(k, v)
+	}
+	return req
+}
+
+func TestRouterResolvesOrigin(t *testing.T) {
+	t.Parallel()
+	spoofed := map[string]string{forwarded.HeaderFor: "203.0.113.7", forwarded.HeaderProto: "https"}
+	tests := []struct {
+		name string
+		peer string
+		want string
+	}{
+		{"trusted proxy's forwarded headers are honoured", traefik + ":41000", "203.0.113.7 https"},
+		{"untrusted peer spoofing them is ignored", "198.51.100.9:5000", "198.51.100.9 http"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			rec := httptest.NewRecorder()
+			newOriginRouter(t, io.Discard).ServeHTTP(rec, originRequest("/auth/probe", tt.peer, spoofed))
+			if rec.Code != http.StatusOK || rec.Body.String() != tt.want {
+				t.Errorf("probe = %d %q, want 200 %q", rec.Code, rec.Body.String(), tt.want)
+			}
+		})
+	}
+}
+
+func TestRouterLogsResolvedClientIP(t *testing.T) {
+	t.Parallel()
+	spoofed := map[string]string{forwarded.HeaderFor: "203.0.113.7", forwarded.HeaderProto: "https"}
+	tests := []struct {
+		name string
+		peer string
+		want string
+	}{
+		{"trusted proxy", traefik + ":41000", "203.0.113.7"},
+		{"untrusted peer spoofing", "198.51.100.9:5000", "198.51.100.9"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			var logs bytes.Buffer
+			// A failed session lookup is logged with the request's context.
+			req := originRequest("/api/v1/me", tt.peer, spoofed)
+			req.AddCookie(brokenSessionCookie)
+			rec := httptest.NewRecorder()
+			newOriginRouter(t, &logs).ServeHTTP(rec, req)
+			if rec.Code != http.StatusInternalServerError {
+				t.Fatalf("status = %d, want 500", rec.Code)
+			}
+			var line map[string]any
+			if err := json.Unmarshal(logs.Bytes(), &line); err != nil {
+				t.Fatalf("log %q: %v", logs.String(), err)
+			}
+			if line["msg"] != "look up session" || line[forwarded.LogAttr] != tt.want {
+				t.Errorf("log = %v, want the session error with %s=%s", line, forwarded.LogAttr, tt.want)
+			}
+		})
+	}
+}
+
+func TestRouterRejectsMalformedForwardedHeaders(t *testing.T) {
+	t.Parallel()
+	const badRequestJSON = `{"error":{"code":"bad_request","message":"invalid forwarded headers","retryable":false}}`
+	for _, headers := range []map[string]string{
+		{forwarded.HeaderFor: "not-an-ip"},
+		{forwarded.HeaderProto: "ftp"},
+	} {
+		var logs bytes.Buffer
+		rec := httptest.NewRecorder()
+		newOriginRouter(t, &logs).ServeHTTP(rec, originRequest("/health", traefik+":41000", headers))
+		if rec.Code != http.StatusBadRequest || rec.Body.String() != badRequestJSON {
+			t.Errorf("%v: response = %d %s, want 400 %s", headers, rec.Code, rec.Body.String(), badRequestJSON)
+		}
+		if !bytes.Contains(logs.Bytes(), []byte("rejected forwarded headers")) {
+			t.Errorf("%v: logs = %q, want the rejection logged", headers, logs.String())
+		}
+
+		// The same headers from an untrusted peer are not examined at all.
+		rec = httptest.NewRecorder()
+		newOriginRouter(t, io.Discard).ServeHTTP(rec, originRequest("/health", "198.51.100.9:5000", headers))
+		if rec.Code != http.StatusOK {
+			t.Errorf("%v from an untrusted peer: status = %d, want 200", headers, rec.Code)
+		}
+	}
+}

internal/server/server.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/go-chi/chi/v5"
 
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/forwarded"
 	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/frontend"
 )
 
@@ -16,9 +17,18 @@ import (
 // SPA's index.html.
 var reservedPrefixes = []string{"/api", "/auth", "/media", "/health"}
 
-// NewRouter returns the HTTP handler for the service. version is reported by
-// GET /health; assets is the web build served for every other GET.
-func NewRouter(logger *slog.Logger, version string, assets fs.FS) (http.Handler, error) {
+// RouteMounter registers its own routes on the router.
+type RouteMounter interface {
+	Mount(r chi.Router)
+}
+
+// NewRouter returns the HTTP handler for the service. Every request first
+// has its client address and scheme resolved, honouring forwarded headers
+// only from a peer in trusted (see resolveOrigin). version is reported by
+// GET /health; auth mounts the /auth routes; sessions guards /api/v1 and
+// /media; assets is the web build served for every other GET. /health, /auth
+// and the web build are public. Requests to /api/v1 other than GET also need the session's CSRF token in CSRFHeader.
+func NewRouter(logger *slog.Logger, version string, trusted forwarded.Trusted, auth RouteMounter, sessions SessionLookup, assets fs.FS) (http.Handler, error) {
 	notFound := apiErrorHandler(logger, http.StatusNotFound, "not_found", "not found")
 	methodNotAllowed := apiErrorHandler(logger, http.StatusMethodNotAllowed, "method_not_allowed", "method not allowed")
 
@@ -28,16 +38,31 @@ func NewRouter(logger *slog.Logger, version string, assets fs.FS) (http.Handler,
 	}
 
 	r := chi.NewRouter()
+	r.Use(resolveOrigin(logger, trusted))
 	r.MethodNotAllowed(methodNotAllowed)
 	r.NotFound(notFound)
 
 	r.Get("/health", health(logger, version))
+	auth.Mount(r)
+	// The session middleware wraps the whole /api/v1 and /media subrouters
+	// rather than being added with Use: chi skips a subrouter's middleware
+	// when it has no routes, which would leave it unguarded.
+	signedIn := requireSession(logger, sessions)
+	csrf := requireCSRF(logger)
+	apiV1, media := chi.NewRouter(), chi.NewRouter()
+	for _, sub := range []*chi.Mux{apiV1, media} {
+		sub.MethodNotAllowed(methodNotAllowed)
+		sub.NotFound(notFound)
+	}
+	apiV1.Get("/me", me(logger))
 	r.Route("/api", func(r chi.Router) {
 		r.MethodNotAllowed(methodNotAllowed)
 		r.NotFound(notFound)
+		r.Mount("/v1", signedIn(csrf(apiV1)))
 	})
-	// Catch-all for the PWA. /auth and /media have no routes yet; the frontend
-	// handler passes them to notFound rather than the SPA fallback.
+	r.Mount("/media", signedIn(media))
+	// Catch-all for the PWA. Unknown /auth paths reach the frontend handler,
+	// which passes them to notFound rather than the SPA fallback.
 	r.Method(http.MethodGet, "/*", web)
 	r.Method(http.MethodHead, "/*", web)
 	return r, nil

internal/server/server_test.go

@@ -10,6 +10,8 @@ import (
 	"strings"
 	"testing"
 	"testing/fstest"
+
+	"github.com/go-chi/chi/v5"
 )
 
 const (
@@ -25,13 +27,39 @@ func newTestRouter(t *testing.T, version string) http.Handler {
 		"index.html":             {Data: []byte(fixtureIndex)},
 		"assets/index-AbC123.js": {Data: []byte(fixtureAsset)},
 	}
-	r, err := NewRouter(logger, version, assets)
+	r, err := NewRouter(logger, version, nil, stubAuth{}, stubSessions{}, assets)
 	if err != nil {
 		t.Fatal(err)
 	}
 	return r
 }
 
+// stubAuth mounts a fixed GET /auth/login in place of the real auth flow.
+type stubAuth struct{}
+
+func (stubAuth) Mount(r chi.Router) {
+	r.Get("/auth/login", func(w http.ResponseWriter, _ *http.Request) {
+		io.WriteString(w, "stub login")
+	})
+}
+
+func TestAuthRoutesMounted(t *testing.T) {
+	t.Parallel()
+
+	router := newTestRouter(t, "dev")
+	rec := httptest.NewRecorder()
+	router.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, "/auth/login", nil))
+	if rec.Code != http.StatusOK || rec.Body.String() != "stub login" {
+		t.Errorf("GET /auth/login = %d %q, want the mounted handler", rec.Code, rec.Body.String())
+	}
+
+	rec = httptest.NewRecorder()
+	router.ServeHTTP(rec, httptest.NewRequest(http.MethodPost, "/auth/login", nil))
+	if rec.Code != http.StatusMethodNotAllowed {
+		t.Errorf("POST /auth/login status = %d, want 405", rec.Code)
+	}
+}
+
 func TestHealth(t *testing.T) {
 	t.Parallel()
 
@@ -98,8 +126,10 @@ func TestReservedPathsNotFound(t *testing.T) {
 	}{
 		{http.MethodGet, "/api"},
 		{http.MethodGet, "/api/unknown"},
+		{http.MethodGet, "/api/v1/unknown"},
+		{http.MethodPost, "/api/v1/unknown"},
 		{http.MethodPost, "/api/unknown"},
-		{http.MethodGet, "/auth/callback"},
+		{http.MethodGet, "/auth/unknown"},
 		{http.MethodGet, "/media/photo.jpg"},
 		{http.MethodGet, "/health/deep"},
 		{http.MethodGet, "/auth/../quests/42"},
@@ -109,8 +139,13 @@ func TestReservedPathsNotFound(t *testing.T) {
 		t.Run(tt.method+" "+tt.path, func(t *testing.T) {
 			t.Parallel()
 
+			// Signed in with the CSRF token, so /api/v1 and /media reach
+			// their routers.
+			req := httptest.NewRequest(tt.method, tt.path, nil)
+			req.AddCookie(validSessionCookie)
+			req.Header.Set(CSRFHeader, testSession.CSRFToken)
 			rec := httptest.NewRecorder()
-			router.ServeHTTP(rec, httptest.NewRequest(tt.method, tt.path, nil))
+			router.ServeHTTP(rec, req)
 
 			if rec.Code != http.StatusNotFound {
 				t.Errorf("status = %d, want 404", rec.Code)

internal/server/session.go

@@ -0,0 +1,37 @@
+package server
+
+import (
+	"errors"
+	"log/slog"
+	"net/http"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/auth"
+)
+
+// SessionLookup finds the live session a request carries; it returns
+// auth.ErrNoSession when there is none. *auth.SessionManager implements it.
+type SessionLookup interface {
+	SessionFor(r *http.Request) (auth.Session, error)
+}
+
+// requireSession is the RequireSession middleware. It passes requests with a
+// live session to next with the session in the context (read it with
+// auth.SessionFrom or auth.ActorFrom); others get 401 unauthenticated.
+func requireSession(logger *slog.Logger, sessions SessionLookup) func(http.Handler) http.Handler {
+	unauthenticated := apiErrorHandler(logger, http.StatusUnauthorized, "unauthenticated", "sign in required")
+	internal := apiErrorHandler(logger, http.StatusInternalServerError, "internal", "internal error")
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			s, err := sessions.SessionFor(r)
+			switch {
+			case errors.Is(err, auth.ErrNoSession):
+				unauthenticated(w, r)
+			case err != nil:
+				logger.ErrorContext(r.Context(), "look up session", "error", err)
+				internal(w, r)
+			default:
+				next.ServeHTTP(w, r.WithContext(auth.WithSession(r.Context(), s)))
+			}
+		})
+	}
+}

internal/server/session_test.go

@@ -0,0 +1,152 @@
+package server
+
+import (
+	"errors"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"slices"
+	"testing"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/auth"
+)
+
+const (
+	unauthenticatedJSON = `{"error":{"code":"unauthenticated","message":"sign in required","retryable":false}}`
+	internalJSON        = `{"error":{"code":"internal","message":"internal error","retryable":false}}`
+)
+
+var (
+	validSessionCookie  = &http.Cookie{Name: auth.SessionCookieName, Value: "valid"}
+	brokenSessionCookie = &http.Cookie{Name: auth.SessionCookieName, Value: "broken"}
+	testSession         = auth.Session{
+		Subject:   "user-123",
+		Email:     "cook@example.com",
+		Name:      "Home Cook",
+		Groups:    []string{"mealquest-admin"},
+		CSRFToken: "csrf-token-123",
+	}
+)
+
+// stubSessions knows one valid session cookie; the broken cookie fails the
+// lookup as a database error would.
+type stubSessions struct{}
+
+func (stubSessions) SessionFor(r *http.Request) (auth.Session, error) {
+	c, err := r.Cookie(auth.SessionCookieName)
+	switch {
+	case err != nil:
+		return auth.Session{}, auth.ErrNoSession
+	case c.Value == validSessionCookie.Value:
+		return testSession, nil
+	case c.Value == brokenSessionCookie.Value:
+		return auth.Session{}, errors.New("database down")
+	default:
+		return auth.Session{}, auth.ErrNoSession
+	}
+}
+
+func TestProtectedPathsRequireSession(t *testing.T) {
+	t.Parallel()
+
+	router := newTestRouter(t, "dev")
+	for _, tc := range []struct {
+		method, path string
+		cookie       *http.Cookie
+	}{
+		{http.MethodGet, "/api/v1/settings/household", nil},
+		{http.MethodPatch, "/api/v1/settings/household", nil},
+		{http.MethodGet, "/api/v1", nil},
+		{http.MethodGet, "/media/photo.jpg", nil},
+		{http.MethodGet, "/api/v1/settings/household", &http.Cookie{Name: auth.SessionCookieName, Value: "unknown"}},
+	} {
+		t.Run(tc.method+" "+tc.path, func(t *testing.T) {
+			t.Parallel()
+			req := httptest.NewRequest(tc.method, tc.path, nil)
+			if tc.cookie != nil {
+				req.AddCookie(tc.cookie)
+			}
+			rec := httptest.NewRecorder()
+			router.ServeHTTP(rec, req)
+
+			if rec.Code != http.StatusUnauthorized {
+				t.Errorf("status = %d, want 401", rec.Code)
+			}
+			if ct := rec.Header().Get("Content-Type"); ct != "application/json" {
+				t.Errorf("Content-Type = %q, want application/json", ct)
+			}
+			if got := rec.Body.String(); got != unauthenticatedJSON {
+				t.Errorf("body = %s, want %s", got, unauthenticatedJSON)
+			}
+		})
+	}
+}
+
+func TestPublicPathsNeedNoSession(t *testing.T) {
+	t.Parallel()
+
+	router := newTestRouter(t, "dev")
+	for _, path := range []string{"/health", "/auth/login", "/", "/assets/index-AbC123.js", "/quests/42"} {
+		t.Run(path, func(t *testing.T) {
+			t.Parallel()
+			rec := httptest.NewRecorder()
+			router.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, path, nil))
+			if rec.Code != http.StatusOK {
+				t.Errorf("GET %s without a cookie = %d, want 200", path, rec.Code)
+			}
+		})
+	}
+}
+
+func TestSessionLookupFailure(t *testing.T) {
+	t.Parallel()
+
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/settings/household", nil)
+	req.AddCookie(brokenSessionCookie)
+	rec := httptest.NewRecorder()
+	newTestRouter(t, "dev").ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusInternalServerError || rec.Body.String() != internalJSON {
+		t.Errorf("response = %d %s, want 500 %s", rec.Code, rec.Body.String(), internalJSON)
+	}
+}
+
+func TestRequireSessionAttachesActor(t *testing.T) {
+	t.Parallel()
+
+	var got auth.Actor
+	var ok bool
+	next := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		got, ok = auth.ActorFrom(r.Context())
+		w.WriteHeader(http.StatusNoContent)
+	})
+	h := requireSession(slog.New(slog.NewTextHandler(io.Discard, nil)), stubSessions{})(next)
+
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/settings/household", nil)
+	req.AddCookie(validSessionCookie)
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusNoContent {
+		t.Fatalf("status = %d, want the handler's 204", rec.Code)
+	}
+	if !ok || got.Subject != "user-123" || got.Email != "cook@example.com" || got.Name != "Home Cook" ||
+		!slices.Equal(got.Groups, []string{"mealquest-admin"}) {
+		t.Errorf("actor = %+v (ok=%v), want the session's household member", got, ok)
+	}
+}
+
+func TestRequireSessionStopsUnauthenticated(t *testing.T) {
+	t.Parallel()
+
+	called := false
+	next := http.HandlerFunc(func(http.ResponseWriter, *http.Request) { called = true })
+	h := requireSession(slog.New(slog.NewTextHandler(io.Discard, nil)), stubSessions{})(next)
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, "/api/v1/settings/household", nil))
+
+	if called || rec.Code != http.StatusUnauthorized {
+		t.Errorf("handler called = %v, status = %d; want not called and 401", called, rec.Code)
+	}
+}