title: Store and retrieve facebook access token in ASP.NET MVC 5 app using OWIN
body: <p>I'm a newbie with OWIN. Currently i'm using visual studio 2015 to create ASP.NET MVC project, and visual studio wizard handle almost of basic functions like register new user, login with external accounts... 
  In Startup.Auth.cs i implemented the login with facebook function as following: </p>
  
  <pre><code>var option = new FacebookAuthenticationOptions
          {
              AppId = appId,
              AppSecret = appSecret,
              Provider = new FacebookAuthenticationProvider()
              {
                  OnAuthenticated = (ctx) =&gt;
                  {
                      ctx.Identity.AddClaim(new System.Security.Claims.Claim("fb_access_token", ctx.AccessToken, ClaimValueTypes.String, "Facebook"));
                      return Task.FromResult(0);
                  }
              },
              AuthenticationType = DefaultAuthenticationTypes.ExternalCookie
          };
          app.UseFacebookAuthentication(option);
  </code></pre>
  
  <p>In AccountController.cs i want to get the access token to fetch some user's information, but i always receive a null reference exception of claim object:</p>
  
  <pre><code>public ActionResult Test()
  {
      ClaimsIdentity claimIdenties = HttpContext.User.Identity as ClaimsIdentity;
      var claim = claimIdenties.FindFirst("fb_access_token");
      return View(claim.Value);
  }
  </code></pre>
  
  <p>Can you guys suggest me any solution? </p>
  
  <p>Sorry i'm not good at English</p>