title: RubyOnRails kind of Single Sign On strategy for devise
body: <p>I want approved external site users to have access in my app automaticaly.</p>
  
  <p>So i have trusted external sites, and i want to have their users atomaticaly have a user on my site. So there would be no need to approve anything per user, only per site...</p>
  
  <p>How to do this in Devise? Omniauth?</p>