Perform 2-factor authentication using duosecurity.com

EdgeAuth is an authentication solution

Email based authentication with mobile devices

Rails plugin for simple Facebook session authentication

Allow authentication via an application token

A gem that provides authentication by JWT(json web token) with faye.

Add support of OpenStack V3 authentication

Authentication layer for OmniAuth

Google Apps authentication

bridge for supporting multiple google authentication libraries

Use Kong OAuth2 Authentication with Grape.

A devise omniauth adapter for Rails apps, using Columbia University authentication.

Hatena Authentication API.

Koho API client for REST interface. Requires authentication token.

Authentication solution for Rails 3 based on JWT

Client certificate authentication for RSolr

HMAC authentication stuff

A ruby gem for Minecraft account authentication.

Service-oriented authentication for Ruby apps

A little gem to get the current multi-factor authentication key on a Mac