plugin:github:github MCP server fails with HTTP 400 "missing required Authorization header"

Description

The plugin:github:github MCP server consistently fails to connect with an HTTP 400 error.

Error

Failed to reconnect to plugin:github:github: HTTP 400 at https://api.githubcopilot.com/mcp/

When inspecting the raw response body directly, it returns:

{"message":"Unrecognized client_id"}

(seen when testing the underlying OAuth client_id used for the handshake)

Steps tried (none resolved it)

1. /mcp → reconnect → fails with the 400 above
2. /plugin → update github plugin → /reload-plugins → still fails
3. /plugin → uninstall github → reinstall → /reload-plugins → still fails

Note on scope

This is not a local credential issue — gh auth login via the GitHub CLI succeeds independently and authenticates fine against github.com. The failure is isolated to the Claude Code plugin's own OAuth handshake against https://api.githubcopilot.com/mcp/, which appears to be sending or expecting a client_id/Authorization header that the server does not recognize.

Environment

• Platform: macOS (Darwin), arm64
• Reload output: Reloaded: 11 plugins · 12 skills · 16 agents · 18 hooks · 4 plugin MCP servers · 0 plugin LSP servers