public override void Invoke(AWSCredentials creds, RegionEndpoint region, int maxItems)
        {
            AmazonCertificateManagerConfig config = new AmazonCertificateManagerConfig();

            config.RegionEndpoint = region;
            ConfigureClient(config);
            AmazonCertificateManagerClient client = new AmazonCertificateManagerClient(creds, config);

            ListCertificatesResponse resp = new ListCertificatesResponse();

            do
            {
                ListCertificatesRequest req = new ListCertificatesRequest
                {
                    NextToken = resp.NextToken
                    ,
                    MaxItems = maxItems
                };

                resp = client.ListCertificates(req);
                CheckError(resp.HttpStatusCode, "200");

                foreach (var obj in resp.CertificateSummaryList)
                {
                    AddObject(obj);
                }
            }while (!string.IsNullOrEmpty(resp.NextToken));
        }