C# 解决“因为算法不同，客户端和服务器无法通信”的问题

故障现象

开发运行环境

解决

实现携带证书的 API URL调用

其它

故障现象

实现微信退款功能，我们需要在微信支付商户后台申请安全证书，并调用退款API URL。在调试过程中为增添返回调试信息属性，重新对.net FrameWorkd 类库进行编译并部署，调试一切正常，但再次覆盖的时候，调用显示为 “ 因为算法不同，客户端和服务器无法通信。” ，系统返回错误：

类似调用如下代码：

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);

问题出在 PostXmlAndCertToUrl 调用上，cert 为申请证书的存放位置，passwrd 为证书密码。

开发运行环境

操作系统： Windows Server 2019 DataCenter

.net版本： .netFramework4.7.2

开发工具：VS2019 C#

解决

System.Net.ServicePointManager.SecurityProtocol 属性可选择安全套接字层 (SSL) 或传输层安全 (TLS) 协议的版本，可能是由于协议版本不匹配造成的此原因，通过在Page_Load 服务器事件添加如下语句，问题解决：

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

}

实现携带证书的 API URL调用

PostXmlAndCertToUrl 实现了携带安全证书访问 API 的能力，说明见下表：

序号	参数名	类型	说明
1	url	string	要访问的 API URL 地址
2	post_data	string	要 POST 的指定规则内容
3	cert	string	API 安全证书存放存储的全路径地址
4	password	string	证书密码

实现代码如下：

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;
}