Rails 3 - Use only OpenID authentication

Question

I want to add authentication to my Ruby on Rails 3 app, but I only need users to be able to authenticate using their Google accounts, because I'm making it a hosted app for the Chrome Webstore, so I think OpenID would work well for this. I want to have some custom fields in the user database to store user-specific data. What should I use for this? I want users to be able to sign up only with OpenID. Thanks.