GmailAPIdotNET.cs

public async Task ListLabels()
{

    UserCredential credential;
    using (var stream = new FileStream("client_secrets_desktop.json", FileMode.Open, FileAccess.Read))
    {
        credential = await GoogleWebAuthorizationBroker.AuthorizeAsync(GoogleClientSecrets.Load(stream).Secrets,
            new[] { GmailService.Scope.GmailReadonly },
            "user", CancellationToken.None);
    }
  
    var service = new GmailService(new BaseClientService.Initializer()
    {
        HttpClientInitializer = credential,
        ApplicationName = "Gmail Test",
    });

    try
    {
        ListLabelsResponse response = service.Users.Labels.List("me").Execute();
        foreach (Label label in response.Labels.OrderBy(p=>p.Name))
        {
            Console.WriteLine(label.Id + " - " + label.Name);
        }
    }
    catch (Exception e)
    {
        Console.WriteLine("An error occurred: " + e.Message);
    }
}