【SSL】WebClient 请求 https 页面出错:未能创建 SSL/TLS 安全通道

#问题：

　　当向一个https的url上发送请求，报错：未能创建 SSL/TLS 安全通道；

using (WebClient client = new WebClient())
{
    string address="https://xxx.com";
    client.Headers.Add(HttpRequestHeader.ContentType, "text/xml");

    System.Text.ASCIIEncoding  encoding=new System.Text.ASCIIEncoding();
    var response = client.UploadData(address, "POST", encoding.GetBytes(msg));
}

 #原因：

　　ssl证书不受信任，验证失败；

#解决方案：

　　请求之前，进行如下设置；

ServicePointManager.ServerCertificateValidationCallback += new System.Net.Security.RemoteCertificateValidationCallback(bypassAllCertificateStuff);

private static bool bypassAllCertificateStuff(object sender, X509Certificate cert, X509Chain chain, System.Net.Security.SslPolicyErrors error)
{
   return true;
}

　　简写

ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };

　　整合

public class Test
{
    public void TestFun
    {
 5　　　　　　　ServicePointManager.ServerCertificateValidationCallback = new System.Net.Security.RemoteCertificateValidationCallback(CheckValidationResult);
　　　　　　 using (WebClient client = new WebClient())
　　　　　　{
   　　　　　  string address="https://xxx.com";
　　　　　　　  client.Headers.Add(HttpRequestHeader.ContentType,"text/xml");
   　　　　　　System.Text.ASCIIEncoding  encoding=new System.Text.ASCIIEncoding();
   　　　　　　var response = client.UploadData(address, "POST", encoding.GetBytes(msg));
　　　　　　}
    } 
    private bool CheckValidationResult(object sender, System.Security.Cryptography.X509Certificates.X509Certificate certificate, System.Security.Cryptography.X509Certificates.X509Chain chain, System.Net.Security.SslPolicyErrors errors)
    {   // 总是接受 认证平台 服务器的证书
        return true;
    }
}