devise
RecommendedFlexible authentication solution for Rails with Warden
Authentication
has_secure_password
Provides Rails 4 has_secure_password mixin for Rails 2. Requires Rails 2.1 or higher.
omniauth
A generalized Rack framework for multiple-provider authentication.
doorkeeper
Doorkeeper is an OAuth 2 provider for Rails and Grape.
authlogic
An unobtrusive ruby authentication library based on ActiveRecord.
clearance
Clearance is built to support authentication and authorization via an email/password sign-in mechanism in applications. It provides some core classes commonly used for these features, along with some opinionated defaults - but is intended to be easy to override.
switch_user
Easily switch current user to speed up development
sorcery
Provides common authentication needs such as signing in/out, activating by email and resetting password.
oath
simple rails authentication
rack-cas
Simple CAS authentication for Rails, Sinatra or any Rack-based site