title: Cross-Domain single sign-on with azure, ACS, Sharepoint 2010, MVC Site, and WebService
body: <p>I have a SharePoint 2010 site configured to login with ACS. And ACS configured to use my own Identity provider. I also have a MVC web application which is also claims aware, and uses ACS for authentication.
  The Idea is to expose certian services from sharepoint, to the MVC site, using the webservice I have build.</p>
  
  <p><a href="http://i.stack.imgur.com/B084s.jpg" rel="nofollow">Here is a Drawing of the Idea:</a></p>
  
  <p>My Idea was That once you log in to the MVC site you could use that SAML token(idenity) to log on to SharePoint(i just pass the SAML Token to the web service, and the service attempts to log in to SharePoint with that token). I was hoping since I configured The Relying Parties(MVC site, SharePoint) in ACS to use the same certificate for signing, it would accept the token even if it was from a different realm. But that isn't the case. So I was wondering how my web service could impersonate the user with the claims I have. I've been doing endless Research, and i'm pretty convinced this just isn't possible. The real question is, if there is a way for SharePoint to trust the tokens I get on my MVC site, without building an entire STS and having SharePoint have a trust relation ship with that. Any Help and ideas would be appreciated.</p>