oauth_provider_not_found

What is it?

This error occurs when Better Auth cannot identify a provider for the callback path—either because the provider segment is missing or because no provider with that id is configured.

Better Auth expects the callback route to be shaped like /api/auth/callback/<provider>. If the <provider> segment is absent (e.g., request hits /api/auth/callback), we cannot determine which integration should handle the callback and the request is rejected.

Common Causes

• Visiting /api/auth/callback directly without the trailing provider segment.

How to resolve

Use the correct callback route shape

• Ensure your application exposes a callback route like /api/auth/callback/[provider] (framework-specific).
• When initiating the OAuth flow, ensure the redirect URI includes the provider segment so the provider returns to /api/auth/callback/<provider>.

Configure infrastructure to preserve the path

• Check proxy/CDN rewrites (Vercel, Cloudflare, Nginx) to make sure they do not strip the final path segment.
• Align trailing slash behavior across environments so that /api/auth/callback/<provider> is preserved.

Avoid manual access to the base callback route

• Do not navigate to /api/auth/callback directly; always start OAuth via Better Auth APIs which generate the correct provider-specific callback URL.

Debug locally

• Inspect the request URL received by your server to confirm the <provider> segment is present.
• Log router/path parameters in your callback handler to verify the provider value.
• Compare environment configs (routes, basePath, rewrites) to ensure the same path structure is used everywhere.

Edge cases to consider

• Trailing slash normalization may alter routing if your framework treats /callback/google/ differently from /callback/google. Configure consistent behavior.