I’m encountering an issue authenticating with the official Figma MCP server (https://mcp.figma.com/mcp) when using Claude Code inside Docker on macOS.
Environment
• macOS (Apple Silicon)
• Docker Desktop
• Claude Code (running inside Docker container)
• MCP server: https://mcp.figma.com/mcp
• Browser: Safari, Chrome, Firefox (all reproduce)
Behavior
• OAuth flow completes in browser
• Redirect to http://localhost:<port>/callback happens
• Then fails with: Browser: Invalid state parameter; Claude: OAuth state mismatch - possible CSRF attack
Notes
• Confirmed callback server is reachable from browser
• Tried: fixed callback port (--callback-port); Docker port mapping; Docker host networking
Observation
The failure happens after a successful redirect to localhost. It appears that the state parameter returned in the callback does not match the original value, causing the request to be rejected.