NextAuth internal endpoints ignore custom basePath configuration

[drac94]

Environment

• next-auth version: 4.24.11
• Next.js version: 14 (App Router)
• Node.js version: 23.11.0
• Browser: Chrome: 138.0.7204.169

Describe the issue

When using NextAuth with a custom basePath configuration in the SessionProvider, internal NextAuth endpoints (like _log) appear to make requests to the default /api/auth path instead of respecting the configured custom path.

Setup

NextAuth route location: app/next-api/auth/[...nextauth]/route.ts

SessionProvider configuration:

<SessionProvider basePath="/next-api/auth">
  {children}
</SessionProvider>

Environment variable:

NEXTAUTH_URL=http://localhost:3000/next-api/auth

Expected behavior

All NextAuth internal requests should use the configured basePath (/next-api/auth/_log, /next-api/auth/_error, etc.)

Actual behavior

NextAuth internal endpoints make requests to /api/auth/_log, /api/auth/_error instead of the configured basePath.

Reproduction

1. Set up NextAuth with App Router in a custom path (e.g., app/next-api/auth/[...nextauth]/route.ts)
2. Configure SessionProvider with basePath="/next-api/auth"
3. Set NEXTAUTH_URL=http://localhost:3000/next-api/auth
4. Use NextAuth in your application
5. Observe requests to /api/auth/_log

Questions

1. Is this expected behavior? Should NextAuth internal endpoints respect the basePath configuration?

2. Is there additional configuration required? Are we missing a configuration option that would make internal endpoints use the custom basePath?