Amazon Cognito vs. Devise vs. OAuth.io

You can create unique identities for your users through a number of public login providers (Amazon, Facebook, and Google) and also support unauthenticated guests. You can save app data locally on users’ devices allowing your applications to work even when the devices are offline.

Devise is a flexible authentication solution for Rails based on Warden

OAuth is a protocol that aimed to provide a single secure recipe to manage authorizations. It is now used by almost every web application. However, 30+ different implementations coexist. OAuth.io fixes this massive problem by acting as a universal adapter, thanks to a robust API. With OAuth.io integrating OAuth takes minutes instead of hours or days.