private async void OnLoad(object sender, Windows.UI.Xaml.RoutedEventArgs e)
        {
            // Try to get Client Id from the Password Vault - if no
            // entry found put up a dialog box to request..
            var appCredentials = GetTokenFromVault(ClientIdResourceName);

            if (string.IsNullOrEmpty(appCredentials.Item1))
            {
                // Put up a UI prompting for the app IDs...
                var cdr = await ClientDialog.ShowAsync();

                if (cdr == ContentDialogResult.Primary)
                {
                    // Wipe out all other cached credentials
                    RemoveTokensFromVault();
                    FileList = new List <ItemViewModel>();

                    ClientId = ClientDialog.ClientId;
                    if (string.IsNullOrEmpty(ClientId))
                    {
                        return;
                    }
                    AddTokenToVault(ClientIdResourceName, ClientId, UserName);
                }
            }
            else
            {
                ClientId = appCredentials.Item1;
            }
        }
        private async void SettingsClick(object sender, Windows.UI.Xaml.RoutedEventArgs e)
        {
            var cdr = await ClientDialog.ShowAsync();

            if (cdr == ContentDialogResult.Primary)
            {
                ClientId = ClientDialog.ClientId;
                if (string.IsNullOrEmpty(ClientId))
                {
                    return;
                }
                AddTokenToVault(ClientIdResourceName, ClientId, UserName);
            }
        }