I don't know of a library for external API integration (so I'll be watching this space), but for OAuth specifically, Omniauth has been invaluable. It supports a

I don't know of a library for external API integration (so I'll be watching this space), but for OAuth specifically, Omniauth has been invaluable. It supports a lot of various strategies [0] which is what it called various OAuth2 implementations. 0: https://github.com/omniauth/omniauth/wiki/List-of-Strategies https://github.com/omniauth/omniauth/wiki/List-of-Strategies