spec: P4-05 — Authelia-specific defaults

Confirmed claim name from the lab IdP is 'groups' (not 'roles' as
the original spec assumed). Default the role_claim config field to
'groups' which also matches Keycloak and Authentik out of the box.
Add a 'display_name' field so the SSO button can read 'Sign in with
Authelia' rather than the generic 'SSO'.

Two new gotchas captured:
  - Authelia 4.39+ 'sub' is an opaque UUID, not username — the
    locked design already keys on sub + reads preferred_username
    for display, so this is just documentation.
  - end_session_endpoint isn't always published (Authelia config-
    dependent); the locked logout flow already degrades cleanly.

docs/superpowers/specs/2026-05-05-p4-05-oidc-design.md

@@ -19,7 +19,7 @@ The Authorization Code flow (with PKCE) is implemented against the discovered we
 | Decision | Pick |
 |---|---|
 | User lifecycle | **B** — JIT-provision local rows on first OIDC login (`auth_source='oidc'`, `oidc_subject`) |
-| Role mapping config | **A** — YAML/env, claim name `roles`, default = deny on no-match |
+| Role mapping config | **A** — YAML/env, claim name configurable (default `groups`, matching Authelia / Keycloak / Authentik), default = deny on no-match |
 | Username source | `preferred_username`, fallback to `email` |
 | Username collision with existing local user | **Refuse** with clear remediation message |
 | Provider config | **Single provider** — `providers:` array can come later |
@@ -51,8 +51,9 @@ oidc:
   issuer:        https://auth.example.com    # well-known config discovered from this
   client_id:     restic-manager
   client_secret: ${RM_OIDC_CLIENT_SECRET}    # or via _FILE
-  scopes:        [openid, profile, email, roles]   # 'roles' usually means a custom scope
+  display_name:  Authelia                    # button label "Sign in with <display_name>"; default "SSO"
-  role_claim:    roles                       # default if absent
+  scopes:        [openid, profile, email, groups]
+  role_claim:    groups                      # default if absent (matches Authelia / Keycloak / Authentik)
   role_mapping:
     rm-admins:    admin
     rm-operators: operator
@@ -196,6 +197,8 @@ The IdP is the hard part to test cleanly. Two layers:
 - **End-session 404 / not advertised** — degrade gracefully; just drop the session and 303 to `/login`. Don't 500 the logout because the IdP doesn't implement RP-initiated logout.
 - **Username changes at the IdP** — silently keep the local username (matches our locked decision: subject is the stable key, username is display-only). Document.
 - **Role claim is sometimes a string, sometimes an array, sometimes a comma-separated string** depending on IdP — normalise into `[]string` before mapping. Authelia/Keycloak emit arrays; some custom setups emit strings; handle both.
+- **Authelia `sub` is an opaque UUID, not the username** (Authelia 4.39+ default for new clients). Don't assume `sub` is human-readable; it's stable but display value is `preferred_username` or `email`. The locked design already keys lookups on `sub` and uses `preferred_username` for the display username, so this is just a correctness note.
+- **`end_session_endpoint` may not be published** (Authelia doesn't advertise it for many configs). The locked logout flow already degrades to "drop session + redirect to /login" when the discovery doc lacks it; no extra config needed.
 - **Password-form bypass for OIDC users via /api/auth/login (JSON)** — same rejection rule applies, not just the HTML form.
 
 ## Acceptance