Devise-omniauth-only-twitter is a project mainly written in RUBY and JAVASCRIPT, it's free.
Example project - authenticates only with Twitter via Omniauth on Devise
== Authenticating via Twitter with Omniauth on Devise
This is an example project on using Devise with Omniauth to authenticate via Twitter, not allowing any other authentication scheme.
This should work with Ruby 1.9.2 & Rails 3.0.9
TODO: Write some tests
== References
http://blog.codegram.com/2011/2/acceptance-tests-with-cucumber-devise-omniauth-and-twitter http://es.asciicasts.com/episodes/235-omniauth-part-1