Login and Auth Broken in Your AI-Built App? Fix It Today

Authentication is one of the most complex features in any web app. AI tools generate auth code that looks correct and often works in simple cases — but breaks in production when users log in on different devices, sessions expire, or OAuth providers enforce strict redirect URL requirements.

Problem: Login Works but User Gets Redirected Back to Login

This is a session persistence issue. The app is not saving the authentication token correctly between page loads. In Supabase apps, this usually means the Supabase client is being recreated on every render instead of being a singleton. Fix: Create the Supabase client once outside any component (in a separate supabase.ts file) and import it everywhere. Never create a new Supabase client inside a component.

Problem: Google or GitHub OAuth Returns an Error

OAuth errors like 'redirect_uri_mismatch' mean the callback URL your app sends does not match what is registered. Fix: Copy the exact callback URL from Supabase → Authentication → Providers → Google → Callback URL and add it to your Google Cloud Console OAuth credentials under Authorised redirect URIs.

Problem: Email Confirmation Link Fails

Users sign up, click the confirmation link, and land on an error. The link is redirecting to localhost or the Lovable preview URL instead of your production domain. Fix: Supabase → Authentication → URL Configuration → update Site URL to your production domain.

Problem: Protected Pages Accessible Without Login

The AI put the auth check in the React component — hiding UI elements if not logged in. But navigating directly to the URL bypasses this entirely. Frontend auth is UX, not security. Fix: Add server-side authentication checks on every API route that returns sensitive data. The backend must verify the user's JWT on every request.

Problem: Session Expires and App Breaks

When a JWT expires, API calls return 401 errors and the app breaks instead of redirecting to login. Fix: Add a Supabase auth state change listener that detects session expiry and redirects to the login page with an appropriate message.

Problem: Multiple Users Seeing Each Other's Data

This is a critical security bug — database queries are not filtering by user ID. Fix: Every query returning user-specific data must include a WHERE user_id filter. In Supabase, implement RLS policies using auth.uid() to automatically scope every query to the current user.

Problem: Logout Does Not Clear the Session

User clicks logout, goes to login page, but clicking back shows the app again. The logout function is only updating local state. Fix: Call supabase.auth.signOut(), clear all local user state, then redirect to login.

Authentication bugs are the highest-priority fixes in any app — they either break the experience entirely or create security vulnerabilities. Fix these before adding any new features.