FreeIPA is an integrated Identity and Authentication solution for Linux/UNIX networked environments. A FreeIPA server provides centralized authentication, authorization and account information by storing data about user, groups, hosts and other objects necessary to manage the security aspects of a network of computers.
A set of unified APIs and tools that instantly enables Single Sign On and user management to all your applications.
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.