title: Multiple MVC5 websites using a single website for authentication (ASP.NET Identity v2)
body: <p>Looking for some guidance on using ASP.NET Identity to provide a single location for logon / authentication across a number of sites (that are all subdomains of a common domain).</p>
  
  <p>The current setup is that I have 2 websites:</p>
  
  <ul>
  <li>site1.example.com</li>
  <li>site2.example.com</li>
  </ul>
  
  <p>They present different views of the system to users, and they share the same backend database, and therefore the same ASP.NET Identity tables.  Logging on via either site logs on via the same db.</p>
  
  <p>What I want to do is unify the logon process via a third site:</p>
  
  <ul>
  <li>auth.example.com</li>
  </ul>
  
  <p>The idea being that the user visits <strong>site1.example.com</strong>, clicks a login button, is redirected to <strong>auth.example.com</strong>, performs the log in, and is redirected back to <strong>site1.example.com</strong>.<br>
  If they then navigated to <strong>site2.example.com</strong>, it would be nice if they were seen to be authenticated already.</p>