title: Google.Apis client for C#sharp auth using refresh token
body: <p>I'm using new beta Google APIs Client Library for .NET to load tasks lists of more than one user. It's classified as "installed aplication" (according to google dev. console) with more than one authorized user accounts. It's really simple to authenticate one user (using google.apis) but I cannot figure out, how to do the same with refresh tokens, and how to use this tokens to get service object.</p>
  
  <p>Sample code:</p>
  
  <pre><code>var credential = GoogleWebAuthorizationBroker.AuthorizeAsync(
              GoogleClientSecrets.Load(GoogleTools.GenerateStreamFromString(GoogleTools.Cred)).Secrets,
  new[] { TasksService.Scope.Tasks },
  "user", CancellationToken.None, new FileDataStore("Tasks.Auth.Store")).Result;         
  
  
  // Create the service.
  service = new TasksService(new BaseClientService.Initializer()
  {
       HttpClientInitializer = credential,
       ApplicationName = "Tasks API Sample",
  });
  </code></pre>
  
  <p>I want to construct object <code>credential</code> using refresh token, but I'm really lost and cannot find any appropriate documentation.</p>