title: SAML: Communication between Service Providers?
body: <p>I've been tasked with writing a SP (Service Provider) for SAML v2.0 in ASP.NET, and I wonder the following;</p>
  
  <p>If a user logs in on the main SP for a service (where my SP becomes accessible for a user as an anchor/link, unless previously bookmarked), and then requests access to my SP, how should I handle their login? </p>
  
  <p>They will have logged in and become authorized by the IdP on the main SP, but how will that SP tell my SP that the user is logged in? 
  Will I have to send a new authorization request to the IdP to determine whether the user is logged in or should it be passed on as post data/redirect with a query string from the SP? </p>
  
  <p>I've read the <a href="http://www.oasis-open.org/committees/download.php/27819/sstc-saml-tech-overview-2.0-cd-02.pdf" rel="nofollow">technical overview</a> as well as the <a href="http://www.oasis-open.org/committees/download.php/20520/SAMLV2.0-basics-Oct2006.pdf" rel="nofollow">basics</a>, but they don't cover this part. </p>
  
  <p><em>I will contact the main SP and ask how to proceed, but I  wanted to cover my bases first and see if there's a standard way on how to deal with this situation.</em></p>