A developer details five critical failure points when integrating Manus OAuth, the authentication backbone for many apps. The guide covers silent killers like exact string matching for redirect URIs, which breaks with trailing slashes. It also addresses the aggressive 7-day refresh token lifetime, which logs users out unexpectedly, unlike longer-lived tokens from providers like Google or GitHub.

The most common error is a CORS failure when developers mistakenly exchange tokens client-side. This exposes the client_secret and violates the OAuth flow, which must happen server-side. Another pitfall is caching user data that fails to sync after profile updates, requiring proactive fetching or webhook implementation to maintain accurate user information.

Persistent sessions are essential, as in-memory storage resets after server restarts, causing a "Session not found" error. The author recommends database-backed sessions using PostgreSQL or Redis for reliability. After implementing these fixes, they reported auth success rates jumping from 87% to 99.2%, proving that OAuth requires ongoing monitoring and not just a one-time setup.