The PKCE verifier cookie, state encoding, redirect-URI construction,
and code exchange were coordinated across three route handlers that
each knew part of the protocol. Two latent bugs lived in the gaps: a
push-initiated re-authorization skipped PKCE entirely (harmless today
only because the sole pusher, Wahoo, is not a PKCE provider), and the
push-resume callback path never cleared the spent verifier cookie.
oauth-flow.server.ts now owns the lifecycle: initiateOAuthFlow builds
the provider redirect (state + verifier cookie, on every entry path),
and completeOAuthFlow consumes the callback — state decode, verifier
recovery, code exchange, connection linking — returning a
discriminated result the route maps to redirects. The three routes are
thin adapters; the next OAuth provider reuses the flow, not the
pattern.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
