authentik/WIP.md

WIP: Go → Rust proxy outpost rewrite

Porting the authentik proxy outpost from Go (internal/outpost/proxyv2) to Rust (src/outpost/proxy). The Rust side has all infrastructure working, but every request handler is todo!() and none of the auth machinery exists yet. We continue in very small steps — each step below is meant to be one focused, compilable, testable commit.

What's already done (Rust)

• Config loading + watch (packages/ak-common/src/config), TLS cert store + self-signed fallback (packages/ak-common/src/tls), generated API client (ak-client).
• OutpostController base + WebSocket event loop (src/outpost/mod.rs, src/outpost/event.rs).
• ProxyOutpost: provider refresh, SNI cert resolution, host→app lookup, HTTP/HTTPS startup (src/outpost/proxy/mod.rs).
• Per-provider Application with router wiring; query-signature dispatcher handle() is done (src/outpost/proxy/application/mod.rs, .../handlers/mod.rs).
• Stack: axum 0.8, tokio, hyper-util, reqwest + reqwest-middleware, rustls/aws-lc-rs (FIPS).

What's stubbed / missing

• todo!(): handle_auth_callback, handle_sign_out, proxy::handle, forward::{caddy,envoy,nginx,traefik}.
• ProxyOutpost::end_session just logs. No /outpost.goauthentik.io/start route.
• No crates/code for: session store (fs + postgres), signed cookies, OAuth2/OIDC client, state JWT, Claims + header injection, bearer introspection + basic/client-credentials auth, TTL auth cache, allowlist regex, reverse-proxy forwarding, error pages.

Locked-in decisions

1. Session store: filesystem first (JSON files in tempdir). Postgres (authentik_providers_proxy_proxysession, sqlx) deferred to a later step.
2. JWT: jsonwebtoken with its aws_lc_rs feature (no ring; keep single FIPS backend). Verify the feature exists at the pinned version when adding it; fall back to a hand-rolled HS256 + aws-lc-rs verifier only if not.
3. Cookies: clean break — axum-extra SignedCookieJar, signing key derived from provider.cookie_secret. Cookie carries only the opaque session ID; not byte-compatible with Go's gorilla securecookie (one-time re-login on cutover, acceptable).
4. OIDC client: hand-rolled with reqwest — form-POSTs for code exchange / introspection / client-credentials + a JWKS GET, mirroring the Go code. No openidconnect/oauth2 crate (API already provides resolved endpoints; avoids discovery + browser/backchannel URL-rewrite friction).
5. Other crates: moka (async) for the 60s auth-header TTL cache; regex (already a workspace dep) for the allowlist.

Key Go references (for parity)

• application/oauth_state.go — state JWT (HS256, iss goauthentik.io/outpost/{client_id}, sid/state/redirect; no exp/aud).
• application/endpoint.go — OIDC endpoint resolution incl. embedded browser vs backchannel host rewriting.
• application/oauth_callback.go, oauth.go — auth start + callback + redirect validation (checkRedirectParam).
• application/auth.go, auth_bearer.go, auth_basic.go — checkAuth order: session → cache → bearer → basic.
• application/mode_common.go — getHeaders (X-authentik-*), basic-auth-from-attributes, IsAllowlisted.
• application/mode_forward.go, mode_proxy.go — the four forward handlers + reverse-proxy data path.
• application/session.go — session options, backend selection, Logout/LogoutSessions.

Incremental steps (each = one focused commit)

Phase A — pure types & crypto primitives (unit-testable, no axum)

• A1. Claims + ProxyClaims serde types (mirror types/claims.go; groups/ entitlements default-empty Vec<String>, raw_token, ak_proxy). Round-trip JSON test.
• A2. Add jsonwebtoken (aws_lc_rs feature). OAuthState type + HS256 encode/decode signed with cookie_secret; disable exp/aud validation, enforce issuer. Tests: round-trip + issuer-mismatch rejection.
• A3. OidcEndpoint struct from OpenIdConnectConfiguration mirroring endpoint.go (embedded/browser URL rewriting). URL-rewrite tests.
• A4. ID-token verification: decode_header→kid, JWKS fetch (reqwest → jwk::JwkSet), RS256 verify; plus HS256-by-client-secret path keyed off id_token_signing_alg_values_supported. Fixture test.

Phase B — session + cookies (needs A1)

• B5. SessionData + async SessionStore trait + FsSessionStore (JSON files, session_<id>, maxage→expiry). save/load/delete/expiry tests.
• B6. Extend Application to hold Arc<dyn SessionStore>, cookie signing key, OidcEndpoint, backchannel reqwest client; wire in Application::new. Compiles, no behavior change.
• B7. Add axum-extra cookie support; signed session-ID cookie read/issue helper with per-provider domain/secure/samesite/path/maxage (mirror getStore options).

Phase C — auth-start + callback (shared flow; needs A2–A4, B)

• C8. /outpost.goauthentik.io/start route + handle_auth_start: ensure session ID, build state JWT, build authorize URL with ?rd=, 302. (First user-visible behavior.)
• C9. redirect_to_start helper: store redirect in session, InterceptHeaderAuth 401 path, forward_domain redirect validation (checkRedirectParam).
• C10. handle_auth_callback: validate state JWT + session-ID match, code exchange, verify ID token, extract claims, session maxage from exp, save, redirect to stored rd.

Phase D — non-session auth paths + caching (needs A4, C)

• D11. Add moka TTL cache; attempt_bearer_auth (introspection POST) + cache get/save (auth_bearer.go, auth.go).
• D12. attempt_basic_auth (goauthentik.io/token username → bearer path; else client-credentials token POST + verify) (auth_basic.go).
• D13. Unified check_auth: session → cache → bearer → basic → Option<Claims>.

Phase E — header injection + allowlist (needs A1)

• E14. get_headers/add_headers (all X-authentik-*, basic-auth from user attributes, additional headers, underscore-dedup). Unit test.
• E15. UnauthenticatedRegex allowlist (IsAllowlisted) — compile regexes in Application::new; mode-dependent path-vs-URL matching. Unit test.

Phase F — modes (needs C, D, E)

• F16. Forward-auth URL helpers (getTraefikForwardUrl, getNginxForwardUrl) + ReportMisconfiguration (events API). Parsing tests.
• F17. handle_traefik + handle_caddy (shared logic): callback/logout dispatch, check_auth→headers, allowlist, else auth-start.
• F18. handle_nginx (200+headers / redirect-flag session save / 401) and handle_envoy (path-trim, host fixup).
• F19. Reverse-proxy data path (mode_proxy.go): hyper-util client → internal_host, request/response modification, backend-override/host-header, streaming, X-Powered-By, check_auth→headers or redirect_to_start.

Phase G — logout, postgres, error pages

• G20. handle_sign_out: clear session, redirect to end_session_endpoint.
• G21. ProxyOutpost::end_session: per-app store logout(sid == event.session_id) (session.go).
• G22. PgSessionStore (sqlx) + feature-flag decision (dep:sqlx under proxy vs new proxy-postgres) + PgPool wiring + backend selection in config schema. DB-gated test.
• G23. Error-page rendering (templated 401/500) replacing bare status codes (error.go).

Ordering risks / notes to carry forward

• AppError is always 502 — return Response directly for 302/401/200 control flow; reserve AppError for genuine internal failures.
• State JWT has no exp — must disable validate_exp/aud in jsonwebtoken::Validation.
• Feature flags: sqlx is currently core-only; decide its gating before G22 so Application field types stay stable (filesystem-first keeps this off the critical path).
• end_session mapping: WS event carries session_id; claim field is sid. FS store must scan-and-match like Go's Logout.
• Embedded backchannel Host override: backchannel client rewrites Host while issuer/jwks use browser host — replicate in A3/A4.
• Tests: use cargo t (project convention), not cargo test --lib.

Verification

• Per step: cargo build + cargo t (the new unit tests for that step). Workspace lints are strict (clippy pedantic/nursery + many restriction lints; unwrap_used/todo/unimplemented = warn) — keep each step clean.
• End-to-end milestone after Phase C: unauthenticated request to a proxy-mode app → 302 to the authorize endpoint; full login loop closes after C10. After Phase F: forward-auth (traefik/nginx) and reverse-proxy modes function against a running authentik core.