Fix OAuth redirect URI and callback errors
OAuth callback errors happen when the redirect URI configured in your OAuth provider doesn't match what your application sends, or when the callback handler fails to exchange the authorization code for tokens.
Error messages you might see
Error: redirect_uri_mismatch - The redirect_uri MUST match the registered callback URL for this application.OAuthCallbackError: Could not parse callback URL parametersWhy this happens in AI-generated code
Redirect URI mismatch between provider and application
AI-generated OAuth config uses localhost URLs that don't match the redirect URIs registered in the OAuth provider (Google, GitHub, etc.), especially after deploying to production.
Missing or incorrect callback route handler
AI tools generate the OAuth initiation flow but create an incomplete or incorrectly structured callback route that fails to exchange the authorization code for tokens.
State parameter mismatch or CSRF validation failure
AI-generated OAuth flows don't properly persist and validate the state parameter across the redirect, causing anti-CSRF checks to fail on callback.
How to fix it
Ensure redirect URIs match exactly
Copy the exact callback URL from your code (including trailing slashes and port numbers) and add it to your OAuth provider's allowed redirect URIs. Update it for each deployment environment.
Implement the complete callback handler
Your callback route must: extract the code parameter, exchange it for tokens via a POST to the provider's token endpoint, validate the state parameter, and create a session.
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Frequently asked questions
Why does OAuth work locally but fail in production?
Your OAuth provider has separate redirect URIs for each environment. You need to add your production URL (e.g., https://myapp.com/api/auth/callback/google) to the provider's allowed URIs alongside localhost.
Do I need to handle the state parameter?
Yes — the state parameter prevents CSRF attacks. Generate a random state before redirecting, store it in a cookie or session, and verify it matches when the provider redirects back to your callback.
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