title: Devise signing out
body: <p>last time, I asked this question I have been misunderstood. So:</p>
  
  <p>In my Rails3 application I use Devise for authentication. I have requirement which says, that every user can be logged in only from one browser. It means if user A is logged in (e.g. on FF), and then from other computer, or from other browser (e.g. Chrome) comes request to log user A, the first one should be logged out.</p>
  
  <p>I found out, that I can override SessionController and it's create method. However I don't see any way to check if user with given email (params[:email]) is currently logged in, furthermore I don't know which method should I invoke to destroy this user session.</p>