Support authentication via OAuth2 tokens dispensed from the Doorkeeper authorization flow

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

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.