GitHub plugin authentication fails - browser window not opening

Description

When attempting to authenticate the GitHub plugin (Plugin:github:github MCP Server) via /plugin, the browser window does not open and authentication fails.

Error Message

Error: Incompatible auth server: does not support dynamic client registration

Plugin Details

• Plugin: Plugin:github:github MCP Server
• Status: Failed
• Auth: Not authenticated
• URL: https://api.githubcopilot.com/mcp/
• Config location: Dynamically configured

Steps to Reproduce

1. Run /plugin in Claude Code CLI
2. Select GitHub plugin
3. Select "Authenticate"
4. Expected: Browser window opens for OAuth authentication
5. Actual: Error shown, browser never opens

Environment

• OS: macOS (Darwin 25.3.0)
• Claude Code Model: Claude Opus 4.6 (1M context)

Screenshots

The plugin status screen shows the error:

Plugin:github:github MCP Server

Status: ✗ failed
Auth: ✗ not authenticated
URL: https://api.githubcopilot.com/mcp/
Config location: Dynamically configured

Error: Incompatible auth server: does not support dynamic client registration

> 1. Authenticate
  2. Reconnect
  3. Disable