title: Method GetTokenAsync unavailable
body: <p>I´m following the Quickstarts from IdentityServer4. When I implement the "Switching to Hybrid Flow and adding API Access back" tutorial, I found that the method to get the access token in line:</p>
  
  <pre><code>ViewContext.HttpContext.Authentication.GetTokenAsync("access_token")
  </code></pre>
  
  <p>is not available. Someone knows what method I must to use? Thanks.</p>