[BUG] Error 400: redirect_uri_mismatch when authenticating Google MCP servers

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When trying to authenticate Google MCP servers (Gmail, Google Calendar, Google
Drive)
via /mcp, Google returns Error 400: redirect_uri_mismatch.

Environment:

• macOS Sequoia (arm64)
• Claude Code (version: see /version)

What Should Happen?

Authentication should complete successfully and the Google MCP server
should connect to the Claude Code session.

Error Messages/Logs

Access blocked: This app's request is invalid.                                
Error 400: redirect_uri_mismatch

Steps to Reproduce

1. Open /mcp in Claude Code
2. Click authenticate on Gmail / Google Calendar / Google Drive
3. Google sign-in page opens, account is selected
4. Error page is shown instead of completing auth

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.140

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Authenticated via claude.ai subscription (not API key).