title: Single sign-on flow using ASP.NET MVC + Active Directory
body: <p>I'm looking into creating a single-sign-on portal built in ASP.NET MVC. This single sign on portal should give users the option to sign in with their individual account (which should be verified against AD) or their Facebook/Twitter account. What I'm still in the dark about is if the application/authentication flow I came up with is actually feasible. This is how it should work:</p>
  
  <p>User logs into the SSOP with his AD account (using a custom form where he enters these credentials). The SSOP verifies these credentials against AD and logs the user into the SSOP accordingly. The SSOP then offers the user to start any of the applications he has access to (based on his group memberships in AD). These applications are built by various third parties and are not all .NET based. Clicking one of these applications in the SSOP should log the user into this application using the credentials authenticated against AD that were used to enter the SSOP. I currently do not know how this should be done, e.g. by using claims or some sort of auth token? Obviously the receiving application should support whatever option we choose, which means we're looking for a best practice of some sorts.</p>
  
  <p>The social login part of the SSOP should work somewhere along the following lines: The user logs in using his social account. The first time he does, he also has to enter his AD account credentials so we can link his social account to a specific AD account. Every subsequent time the user logs in with his social account the SSOP should log in the linked AD user. That way the SSOP always uses a valid AD account to authenticate to the applications it offers the user. This also makes it easier to administrate the user base since these are all stored in AD. The social login links and any other SSOP specific data is stored in a custom data store (MS SQL db).</p>
  
  <p>I've been looking into the ThinkTecture IdentityServer, but have yet to figure out how it can be used in this scenario or if this scenario is even feasible.</p>
  
  <p>So, the question basically is: is this authentication flow even possible or remotely best practice? If so, where to begin? And if not, what is?</p>