title: Automatic Login with Janrain/OneAll/LoginRadius etc
body: <p>I am planning to allow users to login to a website I am developing using their social network logins. Probably using one of the multi-provider services such as Janrain, OneAll, LoginRadius. What I want to know is, if a user of my site is already logged into their social network site when they visit my site, how do I go about automatically signing them in? The example I have come across that does this is goodreads.com.</p>
  
  <p>I've developing in ASP.NET MVC3 but I would welcome any explanations/examples on how I go about this in any technology or even just the theory.</p>