The OAuth 2.0 Authorization Framework draft-ietf-oauth-v2-28 implementation on top of devise.
There are plenty of gems out there that deal with being an OAuth2 "consumer", where you redirect users to an OAuth2 "provider", allowing you to hand off authentication to a separate service. There are also plenty of gems that set you up as your own OAuth2 provider. ***BUT***, what happens when you want to separate your "authentication" server from your "resource" server? This gem is meant to be used on an API "resource" server, where you want to accept OAuth Access Tokens from a client, and validate them against a separate "authentication" server. This communication is outside the scope of the official OAuth 2 spec, but there is a need for it anyway.
Rails3 engine that adds OAuth2 Provider support to any application built with Devise authentication
Rails 4 engine that adds OAuth2 Provider support to any application built with Devise authentication
Devise OAuth2 Facebook extension
Devise OAuth2 Facebook extension
Implements OAuth2 for Devise, specifically integrating with facebook Graph
Devise OAuth2 Facebook extension
add OAuth2 authentication to rails3 application
Devise OAuth2 Facebook extension for rails 3 and mongoid