title: Get expire time of OAuth session
body: <p>To grant or revoke access to my webapis, I use OAuth password- and tokenrefreshworkflow.</p>
  
  <p>If I understand everything correctly the workflow should be something like this:</p>
  
  <ol>
  <li>Authenticate with username / password / client id</li>
  <li>Retrieve accestoken, refreshtoken and expire date</li>
  <li>Start timeout in client to refresh your token after expired token time</li>
  <li>Go on with bullet 2 -> and so on..</li>
  </ol>
  
  <p>The progress above works fine so far. My problem is, that I don't get the expire time out of the users principle after the authentication request. So if I work with stateles webclients, I need to renew my token every request to retrieve a new expire date, even if the users token is valid :/</p>
  
  <p>What I want is something like a /api/session/information service, that provides general information about the current session of an authenticated user.</p>
  
  <p>How do I retrieve my expire date =)</p>
  
  <pre><code>[HttpGet]
  [ActionName("information")]
  public HttpResponseMessage Information(BaseRequest request)
  {
  
      var p = Request.GetRequestContext().Principal;
  
      /* here i need help =) */
  }
  </code></pre>