hitch-rails

https://github.com/tylerklose/hitch-rails

Hitch lets MCP clients -- Claude, ChatGPT, Cursor -- call your Rails app's tools as a specific signed-in user, with access you can revoke. You do not stand up a separate auth server, add Redis, or adopt a new sign-in system. Hitch uses the authentication your app already has (current_user or Current.user) and your configured cache store. Underneath it is a full OAuth 2.1 authorization server implementing the MCP 2026-07-28 authorization profile: PKCE (S256), audience-bound tokens (RFC 8707), discovery metadata (RFC 8414 + RFC 9728), revocation (RFC 7009), Client ID Metadata Documents, and optional Dynamic Client Registration (RFC 7591). It adds an authenticated /mcp endpoint backed by the official Ruby MCP SDK and a deny-default tool registry with schema validation and size caps. SQLite and PostgreSQL supported.