Add GET /oauth/youtube/connect and /oauth/youtube/callback, mounted inside
the login + registration guard so CurrentUserID is always set and every
connection binds to the authenticated tapir user.
- connect: generate a per-user CSRF state (single-use, short TTL, bound to
the user), redirect to Google consent with access_type=offline and
prompt=consent so a refresh token comes back.
- callback: verify the state belongs to this user, exchange the code via the
existing auth.Exchange, persist the refresh token under a PER-USER ref
(web.YouTubeTokenRef = "youtube/<userID>/refresh_token") so tenants never
collide, then UpsertConnection (provider=youtube, status=active). Any
failure renders a clean error page and leaves no half-written state.
Reuses auth.Exchange and adds auth.AuthCodeURL (offline + consent) rather
than the CLI's listener/terminal flow (ADR-006: web flow, not CLI). The
ConnectHandler depends on a narrow web.Connections port, not the concrete
store. Wired in cmdServe only when YT client credentials are present;
TAPIR_YT_CONNECT_REDIRECT_URL configures the callback URL. Per-user token-ref
scheme documented in docs/homelab-integration.md.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
