谷歌日历API和c# - 403禁止

寻求帮助。我已经浏览了所有的文档，SO和Google，但仍然没有运气。

我试图与谷歌日历API集成在我的Web应用程序的"检查可用性"功能。目前我只掌握了最基本的连接，我所能做的就是验证并提取一些数据。我已经包括我的代码下面-所有我得到的是403禁止错误之后，我已经看到了所有的建议。

有谁能指出我哪里错了吗?

public void Page_Load(object sender, EventArgs e)
{
  // Register the authenticator. The Client ID and secret have to be copied from the API Access
  // tab on the Google APIs Console.
  var provider = new NativeApplicationClient(GoogleAuthenticationServer.Description);
  provider.ClientIdentifier = "MY_CLIENT_ID";
  provider.ClientSecret = "MY_SECRET";
  var auth = new OAuth2Authenticator<NativeApplicationClient>(provider, GetAuthentication);
  // Create the service.
  var service = new CalendarService(new BaseClientService.Initializer
  {
      Authenticator = auth
  });
  EventsResource.ListRequest req = service.Events.List("primary");
  if (req != null)
  {
      var events = req.Fetch();
      if (events != null)
      {
          litResult.Text = events.Items.Count().ToString();
      }
      else
      {
          litResult.Text = "Zilch.";
      }
  }
  else
  {
      litResult.Text = "Nada.";
  }
}
private static IAuthorizationState GetAuthentication(NativeApplicationClient arg)
{
  // Get the auth URL:
  IAuthorizationState state = new AuthorizationState(new[] { "https://www.google.com/calendar/feeds" });
  state.Callback = new Uri(NativeApplicationClient.OutOfBandCallbackUrl);
  Uri authUri = arg.RequestUserAuthorization(state);
  // Request authorization from the user (by opening a browser window):
  Process.Start(authUri.ToString());
  Console.Write("  Authorization Code: ");
  string authCode = Console.ReadLine();
  Console.WriteLine();
  // Retrieve the access token by using the authorization code:
  return arg.ProcessUserAuthorization(authCode, state);
}

provider.ClientIdentifier = "MY_CLIENT_ID";
provider.ClientSecret = "MY_SECRET";