Sergio Marin
https://github.com/highercomve/oauth_con_doorkeeper
https://github.com/doorkeeper-gem/doorkeeper/wiki
https://github.com/doorkeeper-gem/doorkeeper/wiki/Client-Credentials-flow
https://github.com/doorkeeper-gem/doorkeeper/wiki/authorization-flow
https://github.com/doorkeeper-gem/doorkeeper/wiki/Using-Resource-Owner-Password-Credentials-flow
https://github.com/doorkeeper-gem/doorkeeper/wiki/Create-a-OmniAuth-strategy-for-your-provider
https://github.com/plataformatec/devise/wiki/OmniAuth:-Overview
By Sergio Marin