A set of unified APIs and tools that instantly enables Single Sign On and user management to all your applications.
MongoDB stores data in JSON-like documents that can vary in structure, offering a dynamic, flexible schema. MongoDB was also designed for high availability and scalability, with built-in replication and auto-sharding.
Devise is a flexible authentication solution for Rails based on Warden
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.
OmniAuth is a Ruby authentication framework aimed to abstract away the difficulties of working with various types of authentication providers. It is meant to be hooked up to just about any system, from social networks to enterprise systems to simple username and password authentication.