ServicePointManager.ServerCertificateValidationCallback += ValidateRemoteCertificate;

            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

        /// <summary>

        /// Certificate validation callback.

        /// </summary>

        private static bool ValidateRemoteCertificate(object sender, X509Certificate cert, X509Chain chain, SslPolicyErrors error)

        {

            // If the certificate is a valid, signed certificate, return true.

            if (error == System.Net.Security.SslPolicyErrors.None)

            {

                return true;

            }

            Console.WriteLine("X509Certificate [{0}] Policy Error: '{1}'",

                cert.Subject,

                error.ToString());

            return false;

        }