Share 'Two-Factor Authentication in your Rails App with Devise & Yubikey'

Most rails applications have some sort of "user" to represent either customers who are consuming the service or administrators that are publishing content to the web application.  It's important that these users are authenticated (ensuring that they are who they say they are).  For user authentication in a Ruby on Rails application, Devise is one of the best solutions out there.  It has a very ac…