[BUG] Claude Code OAuth Authentication Failure

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?

Trying to claude login on a fresh Claude Code installation, but an "Unable to access Claude Code" error occurs immediately on the OAuth authorization page in the browser (https://claude.ai/oauth/authorize?...) preventing any authentication.

<img width="731" height="494" alt="Image" src="https://github.com/user-attachments/assets/5b5856a9-bb3e-4928-9e30-5145b7e17c6e" />

What Should Happen?

When running claude auth login, the OAuth authorization page at https://claude.ai/oauth/authorize should:

1. Load successfully without errors
2. Display the Claude authentication interface
3. Allow user to authenticate with their Claude.ai credentials
4. Redirect back to Claude Code with a valid authorization code
5. Complete the OAuth flow and establish an authenticated session
6. The user should then be able to use Claude Code normally with their authenticated account.

Error Messages/Logs

Steps to Reproduce

Environment:

• macOS and Alpine Docker (fresh container)
• Multiple browsers tested (regular and incognito)
• Different networks tested

Steps Taken:

• claude auth logout and claude auth login
• Completely removed ~/.claude directory
• Full uninstall/reinstall of Claude Code
• Tested in fresh Alpine Docker container (no pre-existing config)
• Manual URL copy method (pressing 'c') attempted
• Verified other https://claude.ai/ pages work normally
• Repeatedly logged out and logged back into my Anthropic "team" account on claude.ai

Key Details:

• Error appears immediately on OAuth page, before any authentication or callback
• Not a network connectivity issue (other claude.ai pages accessible)
• Not a local configuration issue (reproduced in clean Docker environment)
• Error occurs at the OAuth service level, not during callback/redirect
• Expected: OAuth authorization page should allow authentication and redirect back to Claude Code
• Actual: Immediate "Unable to access Claude Code" error on authorization page itself
• This appears to be a service-side OAuth endpoint issue requiring engineering investigation.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.114 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

More details in Conversation ID with Fin AI Agent: 215473969648373