title: BootstrapContext is null on ClaimsIdentity
body: <p>I have created a new ASP.NET MVC application with .NET 4.5. I have successfully set up authentication with an STS. The authentication flow is working fine and I am able to get the ClaimsIdentity, containing the desired claims, on Thread.CurrentPrincipal.</p>
  <p>Now I need the bootstrap token to secure the calls to my service layer. I have set the saveBootstrapContext to true on the identityConfiguration element.</p>
  <pre><code>&lt;system.identityModel&gt;
      &lt;identityConfiguration saveBootstrapContext=&quot;true&quot;&gt;
  </code></pre>
  <p>However, the BootstrapContext property on the ClaimsIdentity is always null.</p>
  <pre><code>var identity = Thread.CurrentPrincipal.Identity as ClaimsIdentity;
  var context = identity.BootstrapContext; // context is always null
  </code></pre>
  <p>Am I missing anything here? This was supposed to be straightforward :(</p>