C#解决“因为算法不同，客户端和服务器无法通信”的问题

string cert = @"D:\wxpay\apiclient_cert.p12";
 
string password = "14302";
 
string post_data = getRefundOrderXml(refundorder, key);
string request_data = PostXmlAndCertToUrl(RefundOrderUrl, post_data,cert,password);

void Page_Load(Object sender, EventArgs e)
{
     System.Net.ServicePointManager.SecurityProtocol = 
System.Net.SecurityProtocolType.Tls | 
System.Net.SecurityProtocolType.Tls11 | 
System.Net.SecurityProtocolType.Tls12;
 
}  

public string PostXmlAndCertToUrl(string url, string postData,string cert,string password)
{
     string resp = string.Empty;
     ServicePointManager.ServerCertificateValidationCallback = new System.Net.Security.RemoteCertificateValidationCallback(CheckValidationResult);
System.Security.Cryptography.X509Certificates.X509Certificate2 cer = new System.Security.Cryptography.X509Certificates.X509Certificate2(cert, password, System.Security.Cryptography.X509Certificates.X509KeyStorageFlags.PersistKeySet | System.Security.Cryptography.X509Certificates.X509KeyStorageFlags.MachineKeySet);
 
     HttpWebRequest webrequest = (HttpWebRequest)HttpWebRequest.Create(url);
     webrequest.ClientCertificates.Add(cer);
     webrequest.Method = "post";
     webrequest.ContentType = "application/x-www-form-urlencoded";
     webrequest.ContentLength = postData.Length;
     HttpWebResponse response = null;
     try
     {
        StreamWriter swRequestWriter = new StreamWriter(webrequest.GetRequestStream());
        swRequestWriter.Write(postData);
 
        if (swRequestWriter != null)
            swRequestWriter.Close();
 
            response = (HttpWebResponse)webrequest.GetResponse();
            using (StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.UTF8))
            {
              resp = reader.ReadToEnd();
            }
     }
     catch (Exception exp)
     {
           throw exp;
                    
     }
     finally
     {
           if (response != null)
               response.Close();
     }
     return resp;
}
 
private static bool CheckValidationResult(object sender, System.Security.Cryptography.X509Certificates.X509Certificate certificate, System.Security.Cryptography.X509Certificates.X509Chain chain, System.Net.Security.SslPolicyErrors errors)
{
       if (errors == System.Net.Security.SslPolicyErrors.None)
           return true;
       return false;
}