NextAuth.js Infinite Redirect Loop on Callback

1. Callback URL mismatch between NextAuth config and OAuth provider settings (trailing slashes, protocol differences)
2. Circular redirect in the authorize callback or jwt callback functions
3. Session validation failing silently, causing re-auth attempts
4. Incorrect NEXTAUTH_URL environment variable or missing NEXTAUTH_SECRET
5. Database session adapter connection issues preventing session creation

Verify callback URLs: Ensure your OAuth provider (GitHub, Google, etc.) has the exact callback URL registered: http://localhost:3000/api/auth/callback/github

Check NextAuth config: Verify NEXTAUTH_URL matches your deployment URL exactly. In development use http://localhost:3000.

Debug redirect logic: Add logging in your callbacks to trace the redirect path. Check for infinite loops in redirect conditions.

Session persistence: If using a database adapter, verify the database connection and that session tables are properly created.