[BUG] Claude Desktop (macOS): "Continue with Google" always ends in "Sign in failed" at claude.ai/login/app-google-auth

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Desktop available to me

What's Wrong?

Claude Desktop on macOS can't sign in with Google. Clicking Continue with Google on the desktop Sign In screen opens the system browser at claude.ai/login/app-google-auth?..., which immediately shows:

Sign in failed Close this window and try again from the desktop app.

Retrying from the desktop app gives the same result every time. The app stays on the Sign In screen.

What Should Happen?

The Google OAuth flow should finish in the browser and hand the session back to the desktop app, which should then be signed in.

Error Messages/Logs

~/Library/Logs/Claude/main.log shows the browser hand-off on each attempt, and nothing after it (no callback or error is logged):

2026-10-12 14:02:18 [info] [Auth] Using system browser for: /login/app-google-auth
2026-10-12 14:02:26 [info] [Auth] Using system browser for: /login/app-google-auth
2026-10-12 14:04:16 [info] [Auth] Using system browser for: /login/app-google-auth

Steps to Reproduce

1. Open Claude Desktop while signed out.
2. Click Continue with Google (marked "Last used").
3. The system browser opens https://claude.ai/login/app-google-auth?....
4. The page shows "Sign in failed — Close this window and try again from the desktop app."

Is this a regression?

I don't know

Environment

• Claude Desktop: 1.49585.0
• OS: macOS 27.0.1 (26A434)
• Auth method: Google

Screenshots

Screenshots of the desktop Sign In screen and the "Sign in failed" browser page are attached below.