Sanitize OIDC discovery errors and require CSRF on HEAD and OPTIONS

F03-01: go-oidc embeds the provider's response body in its error for a
non-200 discovery response, which cmd/server logged at startup. Discovery
now runs through a status-recording transport and a non-200 response is
reported as "provider answered HTTP <status>" only; transport errors keep
their cause. A test with a sentinel body proves it reaches neither the
error nor the log.

F03-02: the CSRF middleware exempts only GET, so HEAD and OPTIONS under
/api/v1 without X-MealQuest-CSRF get 403 csrf, matching CONTEXT.MD.

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

README.md

@@ -40,6 +40,10 @@ export MEALQUEST_OIDC_ALLOWED_GROUPS=mealquest-admin
 # 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
 ```
 
@@ -47,7 +51,8 @@ make dev
 (which proxies `/api`, `/auth` and `/media` to `:8080`). Open
 http://localhost:5173. Configuration is environment-only and fails fast:
 every variable above is required except the commented-out session
-lifetimes (when set they must be positive, with MAX at least IDLE), and
+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]`.

cmd/server/main.go

@@ -15,6 +15,7 @@ import (
 
 	"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/server"
 	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/store"
@@ -31,7 +32,7 @@ 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)
@@ -57,17 +58,18 @@ func run(cfg config.Config, logger *slog.Logger) error {
 		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()),
+		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, authFlow, frontend.Assets())
+	router, err := server.NewRouter(logger, version, cfg.TrustedProxy, authFlow, sessions, frontend.Assets())
 	if err != nil {
 		return err
 	}
@@ -125,6 +127,7 @@ 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 |

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

@@ -12,6 +12,8 @@ import (
 	"log/slog"
 	"net/http"
 	"net/url"
+	"slices"
+	"sync/atomic"
 	"time"
 
 	"github.com/coreos/go-oidc/v3/oidc"
@@ -65,15 +67,20 @@ type Config struct {
 	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
@@ -92,6 +99,8 @@ func New(ctx context.Context, cfg Config, sessions Sessions, logger *slog.Logger
 		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 {
@@ -99,9 +108,12 @@ func New(ctx context.Context, cfg Config, sessions Sessions, logger *slog.Logger
 	}
 
 	client := &http.Client{Timeout: providerTimeout, CheckRedirect: checkRedirect}
-	provider, err := oidc.NewProvider(oidc.ClientContext(ctx, client), cfg.Issuer)
+	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, fmt.Errorf("auth: OIDC discovery: %w", err)
+		return nil, discoveryError(err, int(recorder.status.Load()))
 	}
 	endpoint := provider.Endpoint()
 	var discovered struct {
@@ -118,6 +130,9 @@ func New(ctx context.Context, cfg Config, sessions Sessions, logger *slog.Logger
 		{"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
@@ -138,7 +153,9 @@ func New(ctx context.Context, cfg Config, sessions Sessions, logger *slog.Logger
 			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,
@@ -146,6 +163,32 @@ func New(ctx context.Context, cfg Config, sessions Sessions, logger *slog.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 {
@@ -218,7 +261,9 @@ func (a *Auth) login(w http.ResponseWriter, r *http.Request) {
 }
 
 // callback completes the flow: it checks state against the login cookie,
-// exchanges the code, verifies the ID token and nonce, then starts a session.
+// 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()
@@ -256,6 +301,22 @@ func (a *Auth) callback(w http.ResponseWriter, r *http.Request) {
 		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)
@@ -278,7 +339,8 @@ func (a *Auth) logout(w http.ResponseWriter, r *http.Request) {
 
 // verify exchanges code for tokens and returns the verified ID token claims.
 // The verifier enforces RS256, issuer, audience and expiry; nonce is checked
-// here.
+// 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))
@@ -303,9 +365,50 @@ func (a *Auth) verify(ctx context.Context, code string, state loginState) (Claim
 	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")
+}
+
+// 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.

internal/auth/auth_test.go

@@ -11,6 +11,7 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"errors"
+	"fmt"
 	"io"
 	"log/slog"
 	"maps"
@@ -36,6 +37,9 @@ const (
 
 var testPublicURL = &url.URL{Scheme: "https", Host: "meals.example.com"}
 
+// testAllowedGroups are the household's groups in tests.
+var testAllowedGroups = []string{"mealquest-admin", "mealquest-family"}
+
 // fakeProvider is an OIDC provider serving discovery, JWKS and a token
 // endpoint. Each issued code maps to the ID token the token endpoint returns.
 type fakeProvider struct {
@@ -50,6 +54,12 @@ type fakeProvider struct {
 	// tokenReply, when set, is returned by the token endpoint instead of a
 	// token.
 	tokenReply *tokenReply
+	// userinfo is the userinfo endpoint's response; userinfoHits counts
+	// requests to it.
+	userinfo     map[string]any
+	userinfoHits int
+	// userinfoReply, when set, is returned by the userinfo endpoint instead.
+	userinfoReply *tokenReply
 }
 
 type tokenReply struct {
@@ -73,6 +83,7 @@ func newFakeProvider(t *testing.T) *fakeProvider {
 	mux.HandleFunc("GET /.well-known/openid-configuration", p.discovery)
 	mux.HandleFunc("GET /jwks", p.jwks)
 	mux.HandleFunc("POST /token", p.token)
+	mux.HandleFunc("GET /userinfo", p.userinfoEndpoint)
 	p.srv = httptest.NewServer(mux)
 	t.Cleanup(p.srv.Close)
 	return p
@@ -86,6 +97,7 @@ func (p *fakeProvider) discovery(w http.ResponseWriter, _ *http.Request) {
 		"authorization_endpoint":                p.issuer() + "/authorize",
 		"token_endpoint":                        p.issuer() + "/token",
 		"jwks_uri":                              p.issuer() + "/jwks",
+		"userinfo_endpoint":                     p.issuer() + "/userinfo",
 		"end_session_endpoint":                  p.issuer() + "/end-session/",
 		"response_types_supported":              []string{"code"},
 		"subject_types_supported":               []string{"public"},
@@ -148,6 +160,41 @@ func (p *fakeProvider) token(w http.ResponseWriter, r *http.Request) {
 	})
 }
 
+// userinfoEndpoint checks the access token and returns p.userinfo, which
+// defaults to the test user without a groups claim.
+func (p *fakeProvider) userinfoEndpoint(w http.ResponseWriter, r *http.Request) {
+	if r.Header.Get("Authorization") != "Bearer access-token" {
+		http.Error(w, `{"error":"invalid_token"}`, http.StatusUnauthorized)
+		return
+	}
+	p.mu.Lock()
+	p.userinfoHits++
+	info, reply := p.userinfo, p.userinfoReply
+	p.mu.Unlock()
+	if reply != nil {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(reply.status)
+		io.WriteString(w, reply.body)
+		return
+	}
+	if info == nil {
+		info = map[string]any{"sub": "user-123", "email": "cook@example.com"}
+	}
+	writeJSON(w, info)
+}
+
+func (p *fakeProvider) setUserinfo(info map[string]any) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	p.userinfo = info
+}
+
+func (p *fakeProvider) userinfoRequests() int {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	return p.userinfoHits
+}
+
 // authorize stands in for the user signing in at the provider: it records a
 // code bound to the PKCE challenge and returns it.
 func (p *fakeProvider) authorize(challenge, idToken string) string {
@@ -291,11 +338,12 @@ func newHarness(t *testing.T) *harness {
 	sessions := &memorySessions{}
 	logs := &syncBuffer{}
 	a, err := New(context.Background(), Config{
-		Issuer:       p.issuer(),
-		ClientID:     testClientID,
-		ClientSecret: testClientSecret,
-		PublicURL:    testPublicURL,
-		SecretKey:    []byte("server-secret-key"),
+		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)
@@ -730,28 +778,65 @@ func TestNewFailsWhenDiscoveryFails(t *testing.T) {
 	srv := httptest.NewServer(http.NotFoundHandler())
 	t.Cleanup(srv.Close)
 	_, err := New(context.Background(), Config{
-		Issuer:       srv.URL,
-		ClientID:     testClientID,
-		ClientSecret: testClientSecret,
-		PublicURL:    testPublicURL,
-		SecretKey:    []byte("k"),
+		Issuer:        srv.URL,
+		ClientID:      testClientID,
+		ClientSecret:  testClientSecret,
+		PublicURL:     testPublicURL,
+		SecretKey:     []byte("k"),
+		AllowedGroups: testAllowedGroups,
 	}, &memorySessions{}, slog.New(slog.DiscardHandler))
 	if err == nil {
 		t.Fatal("New succeeded without a discovery document")
 	}
 }
 
+func TestNewDiscoveryErrorOmitsProviderBody(t *testing.T) {
+	t.Parallel()
+	const sentinel = "sentinel-discovery-body-7f3a"
+	for _, status := range []int{http.StatusNotFound, http.StatusInternalServerError} {
+		t.Run(http.StatusText(status), func(t *testing.T) {
+			t.Parallel()
+			srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+				w.WriteHeader(status)
+				io.WriteString(w, sentinel)
+			}))
+			t.Cleanup(srv.Close)
+			logs := &syncBuffer{}
+			_, err := New(context.Background(), Config{
+				Issuer:        srv.URL,
+				ClientID:      testClientID,
+				ClientSecret:  testClientSecret,
+				PublicURL:     testPublicURL,
+				SecretKey:     []byte("k"),
+				AllowedGroups: testAllowedGroups,
+			}, &memorySessions{}, slog.New(slog.NewTextHandler(logs, nil)))
+			if err == nil {
+				t.Fatal("New succeeded without a discovery document")
+			}
+			// cmd/server logs the returned error at startup.
+			slog.New(slog.NewTextHandler(logs, nil)).Error("startup failed", "err", err)
+			if strings.Contains(logs.String(), sentinel) {
+				t.Errorf("logs contain the provider response body: %s", logs)
+			}
+			if want := fmt.Sprintf("auth: OIDC discovery: provider answered HTTP %d", status); err.Error() != want {
+				t.Errorf("error = %q, want %q", err, want)
+			}
+		})
+	}
+}
+
 func TestNewFailsOnIssuerMismatch(t *testing.T) {
 	t.Parallel()
 	p := newFakeProvider(t)
 	// Discovery trims the trailing slash, so this fetches the provider's
 	// document, which reports the issuer without it.
 	_, err := New(context.Background(), Config{
-		Issuer:       p.issuer() + "/",
-		ClientID:     testClientID,
-		ClientSecret: testClientSecret,
-		PublicURL:    testPublicURL,
-		SecretKey:    []byte("k"),
+		Issuer:        p.issuer() + "/",
+		ClientID:      testClientID,
+		ClientSecret:  testClientSecret,
+		PublicURL:     testPublicURL,
+		SecretKey:     []byte("k"),
+		AllowedGroups: testAllowedGroups,
 	}, &memorySessions{}, slog.New(slog.DiscardHandler))
 	if err == nil {
 		t.Fatal("New accepted a provider reporting a different issuer")
@@ -772,11 +857,12 @@ func TestNewRejectsRemoteHTTPIssuer(t *testing.T) {
 	t.Parallel()
 	for _, issuer := range []string{"http://auth.example.com/application/o/mealquest/", "http://192.0.2.10"} {
 		_, err := New(context.Background(), Config{
-			Issuer:       issuer,
-			ClientID:     testClientID,
-			ClientSecret: testClientSecret,
-			PublicURL:    testPublicURL,
-			SecretKey:    []byte("k"),
+			Issuer:        issuer,
+			ClientID:      testClientID,
+			ClientSecret:  testClientSecret,
+			PublicURL:     testPublicURL,
+			SecretKey:     []byte("k"),
+			AllowedGroups: testAllowedGroups,
 		}, &memorySessions{}, slog.New(slog.DiscardHandler))
 		if err == nil || !strings.Contains(err.Error(), "issuer") {
 			t.Errorf("New(issuer %q) error = %v, want issuer rejected", issuer, err)
@@ -793,6 +879,7 @@ func TestNewRejectsRemoteHTTPEndpoint(t *testing.T) {
 		{"token_endpoint", "token endpoint"},
 		{"jwks_uri", "JWKS endpoint"},
 		{"end_session_endpoint", "end session endpoint"},
+		{"userinfo_endpoint", "userinfo endpoint"},
 	}
 	for _, tc := range tests {
 		t.Run(tc.field, func(t *testing.T) {
@@ -800,11 +887,12 @@ func TestNewRejectsRemoteHTTPEndpoint(t *testing.T) {
 			p := newFakeProvider(t)
 			p.discoveryOverrides = map[string]any{tc.field: "http://auth.example.com/" + tc.field}
 			_, err := New(context.Background(), Config{
-				Issuer:       p.issuer(),
-				ClientID:     testClientID,
-				ClientSecret: testClientSecret,
-				PublicURL:    testPublicURL,
-				SecretKey:    []byte("k"),
+				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(), tc.name) {
 				t.Errorf("New error = %v, want %s rejected", err, tc.name)
@@ -840,11 +928,12 @@ func TestCallbackRefusesTokenRedirectToHTTP(t *testing.T) {
 			sessions := &memorySessions{}
 			logs := &syncBuffer{}
 			a, err := New(context.Background(), Config{
-				Issuer:       p.issuer(),
-				ClientID:     testClientID,
-				ClientSecret: testClientSecret,
-				PublicURL:    testPublicURL,
-				SecretKey:    []byte("server-secret-key"),
+				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)

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_test.go

@@ -62,11 +62,12 @@ func newSessionHarness(t *testing.T) *sessionHarness {
 	p := newFakeProvider(t)
 	logs := &syncBuffer{}
 	a, err := New(ctx, Config{
-		Issuer:       p.issuer(),
-		ClientID:     testClientID,
-		ClientSecret: testClientSecret,
-		PublicURL:    testPublicURL,
-		SecretKey:    []byte("server-secret-key"),
+		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)
@@ -490,11 +491,12 @@ func TestNewRequiresEndSessionEndpoint(t *testing.T) {
 	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"),
+		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)

internal/config/config.go

@@ -12,6 +12,7 @@ import (
 	"strings"
 	"time"
 
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/forwarded"
 	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/secureurl"
 )
 
@@ -30,6 +31,8 @@ const (
 
 	EnvSessionIdle = "MEALQUEST_SESSION_IDLE"
 	EnvSessionMax  = "MEALQUEST_SESSION_MAX"
+
+	EnvTrustedProxy = "MEALQUEST_TRUSTED_PROXY"
 )
 
 // Session lifetime defaults (D-004): long enough that the kitchen tablet
@@ -58,6 +61,10 @@ type Config struct {
 	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
@@ -88,6 +95,8 @@ func load(lookup func(string) (string, bool)) (Config, error) {
 
 		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)
@@ -177,6 +186,18 @@ func (r *reader) list(name string) []string {
 	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 {

internal/config/config_test.go

@@ -3,6 +3,7 @@ package config
 import (
 	"errors"
 	"fmt"
+	"net/netip"
 	"net/url"
 	"os"
 	"path/filepath"
@@ -11,6 +12,8 @@ import (
 	"strings"
 	"testing"
 	"time"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/forwarded"
 )
 
 func TestLoad(t *testing.T) {
@@ -293,6 +296,48 @@ func TestLoad(t *testing.T) {
 			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{
@@ -402,8 +447,13 @@ func TestLoadValues(t *testing.T) {
 		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)
@@ -411,6 +461,10 @@ func TestLoadValues(t *testing.T) {
 	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) {

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/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"
 )
 
@@ -21,10 +22,13 @@ type RouteMounter interface {
 	Mount(r chi.Router)
 }
 
-// NewRouter returns the HTTP handler for the service. version is reported by
-// GET /health; auth mounts the /auth routes; assets is the web build served
-// for every other GET.
-func NewRouter(logger *slog.Logger, version string, auth RouteMounter, assets fs.FS) (http.Handler, error) {
+// 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")
 
@@ -34,18 +38,31 @@ func NewRouter(logger *slog.Logger, version string, auth RouteMounter, assets fs
 	}
 
 	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. Unknown /auth paths and /media (no routes yet)
-	// reach the frontend handler, which 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

@@ -27,7 +27,7 @@ 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, stubAuth{}, assets)
+	r, err := NewRouter(logger, version, nil, stubAuth{}, stubSessions{}, assets)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -126,6 +126,8 @@ 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/unknown"},
 		{http.MethodGet, "/media/photo.jpg"},
@@ -137,8 +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)
+	}
+}