[BUG]

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?

Official MCP plugins OAuth callback fails with 404 - localhost callback server unreachable

Description

OAuth authentication for official Claude plugins (@claude-plugins-official) fails because the localhost callback server becomes unreachable before the OAuth redirect completes, resulting in a 404 error.

Affected Plugins

• supabase@claude-plugins-official
• asana@claude-plugins-official

(Likely affects all official plugins using OAuth redirect flow)

Environment

| Field | Value |
|-------|-------|
| macOS version | 26.2 (Build 25C56) |
| Claude Code version | 2.1.29 |
| Shell | zsh |
| Terminal | [fill in: Terminal.app / iTerm / Warp / etc.] |

Debugging Performed

| Check | Result |
|-------|--------|
| macOS Firewall | Disabled (State = 0) |
| Proxy settings | None configured |
| Network filtering tools | None installed (no Little Snitch, Lulu, etc.) |
| VPN | None |

Workaround Confirmation

The Supabase CLI (npx supabase login) works correctly because it uses a verification code flow rather than a redirect callback flow. This confirms the issue is specific to the MCP plugin's OAuth implementation, not the system or network.

Suggested Fix

Consider implementing one of these alternatives:

1. Device code flow (like Supabase CLI) - display a code for users to enter manually
2. Longer timeout on the callback server
3. Token-based auth - allow users to provide personal access tokens via environment variables as an alternative to OAuth

What Should Happen?

The localhost callback server should remain active until the OAuth redirect completes and the token is exchanged.

Error Messages/Logs

The callback URL (e.g., `http://localhost:54321/callback`) returns a 404. The temporary server appears to terminate before the OAuth flow completes.

Steps to Reproduce

1. Enable an official plugin that requires OAuth (e.g., Supabase or Asana) in ~/.claude/settings.json
2. Trigger an action that requires authentication
3. Browser opens to the OAuth provider's login page
4. Complete authentication as quickly as possible
5. OAuth provider redirects to localhost:<random-port>/callback
6. Result: 404 error - the callback server is no longer running

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.29

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_