87c0d024d5
Adds the /__proxy_auth OIDC flow served on every proxied host: - routes/host_auth.js: /start (PKCE+state, per-host redirect_uri), /callback (exchange, enforce the host allow-list via utils/host_sso.identityAllowed, mint session + set __proxy_sso cookie), /logout. - models/sso_session.js: SsoSession (Redis-backed, TTL'd; read directly by the Lua gate) and HostSsoState (in-flight auth request). - utils/oidc.js: per-host redirect_uri override on buildAuthUrl/exchangeCode. - conf.hostSso (reuses conf.oidc). Allow-list logic unit-tested. Enforcement (Lua gate + nginx location) lands next. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>