internal/auth discovers the provider at MEALQUEST_OIDC_ISSUER with
coreos/go-oidc/v3 and runs a confidential-client authorization code flow
with golang.org/x/oauth2 (client_secret_basic).
GET /auth/login stores state, nonce and a PKCE S256 verifier in a
10-minute HMAC-signed HttpOnly __Host- cookie and redirects with scopes
"openid profile email groups offline_access". An optional "return" path
must be same-origin; anything else fails the login with 400.
GET /auth/callback clears the single-use cookie, checks state, exchanges
the code with the verifier, verifies the ID token (RS256 only, issuer,
audience, expiry) and nonce, then hands the claims to a SessionStarter.
cmd/server wires a placeholder that refuses every login until the
session layer lands.
Config gains required MEALQUEST_OIDC_ISSUER, MEALQUEST_OIDC_CLIENT_ID,
MEALQUEST_OIDC_CLIENT_SECRET_FILE and MEALQUEST_OIDC_ALLOWED_GROUPS.
Pins go-oidc v3.21.0 and oauth2 v0.36.0, the newest releases that
support Go 1.25 (oauth2 v0.37.0 requires Go 1.26).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
