title: How to access Facebook private information by using ASP.NET Identity (OWIN)?
body: <p>I am developing a web site in ASP.NET MVC 5 (using RC1 version currently). The site will use Facebook for user authentication and for retrieving initial profile data.</p>
  
  <p>For the authentication system I am using the new OWIN based ASP.NET Identity engine (<a href="http://blogs.msdn.com/b/webdev/archive/2013/07/03/understanding-owin-forms-authentication-in-mvc-5.aspx" rel="nofollow noreferrer">http://blogs.msdn.com/b/webdev/archive/2013/07/03/understanding-owin-forms-authentication-in-mvc-5.aspx</a>), since it greatly simplifies the process of authenticating with external providers.</p>
  
  <p>The problem is that once a user first logs in, I want to get its email address from the Facebook profile, but this data is not included in the generated claims. So I have thought on these alternatives to get the address:</p>
  
  <ol>
  <li><p>Instruct the ASP.NET Identity engine to include the email address in
  the set of data that is retrieved from Facebook and then converted
  to claims. I don't know if this is possible at all.</p></li>
  <li><p>Use the Facebook graph API
  (<a href="https://developers.facebook.com/docs/getting-started/graphapi" rel="nofollow noreferrer">https://developers.facebook.com/docs/getting-started/graphapi</a>) to
  retrieve the email address by using the Facebook user id (which is
  included in the claims data). But this will not work if the user has
  set his email address as private.</p></li>
  <li><p>Use the Facebook graph API, but specifying "me" instead of the
  Facebook user id
  (<a href="https://developers.facebook.com/docs/reference/api/user" rel="nofollow noreferrer">https://developers.facebook.com/docs/reference/api/user</a>). But an
  access token is required, and I don't know how to (or if it's
  possible at all) retrieve the access token that ASP.NET uses to
  obtain the user data.</p></li>
  </ol>
  
  <p>So the question is:</p>
  
  <ol>
  <li><p>How can I instruct the ASP.NET Identity engine to retrieve
  additional information from Facebook and include it in the claims
  data?</p></li>
  <li><p>Or alternatively, how can I retrieve the generated access token so
  that I can ask Facebook myself?</p></li>
  </ol>
  
  <p>Thank you!</p>
  
  <p>Note: for the authentication system my application uses code based on the sample project linked in this SO answer: <a href="https://stackoverflow.com/a/18423474/4574">https://stackoverflow.com/a/18423474/4574</a></p>