我们检测到您的浏览器不兼容传输层安全协议 (TLS) 1.1 或更高版本，此协议在 Internet 上用于确保您通信的安全性。

早上使用.Net WebClient类采集亚马逊数据，返回http 400 Bad Request错误，内容里面有“我们检测到您的浏览器不兼容传输层安全协议 (TLS) 1.1 或更高版本，此协议在 Internet 上用于确保您通信的安全性。”

所以就想着可能是WebClient使用TLS版本过低，查了下资料，全局加上这段代码。

            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;
        }

参考链接：https://stackoverflow.com/questions/20064505/requesting-html-over-https-with-c-sharp-webclient