Asp.Net（旧）：不支持所请求的安全协议

Question

我的应用程序以前使用的是.net 3.5，但后来我将其升级到4.8。

我添加以下代码以支持安全性：

      ServicePointManager.SecurityProtocol|= SecurityProtocolType.SystemDefault|
                                             SecurityProtocolType.Ssl3 |
                                             SecurityProtocolType.Tls |
                                             SecurityProtocolType.Tls11 |
                                             SecurityProtocolType.Tls12 |
                                             SecurityProtocolType.Tls13;

                HttpWebRequest req = WebRequest.Create(HelpURL + path) as HttpWebRequest;
                req.UseDefaultCredentials = true;
                req.PreAuthenticate = true;
                req.Credentials = CredentialCache.DefaultCredentials;

                var statusCode = ((HttpWebResponse)req.GetResponse()).StatusCode;

它适用于https，但不适用于http！

The requested security protocol is not supported

如何允许使用http？

解决方案：

  protected void Page_Load(object sender, EventArgs e)
    {           
        try
        {         
                Uri validatedUri = null;
                var result = Uri.TryCreate(_path, UriKind.RelativeOrAbsolute, out validatedUri);
                if (result)
                {
                    HelpURL = path;

                    if(HelpURL.StartsWith("https://"))
                    {
                        ServicePointManager.SecurityProtocol |= SecurityProtocolType.SystemDefault |
                                                SecurityProtocolType.Ssl3 |
                                                SecurityProtocolType.Tls |
                                                SecurityProtocolType.Tls11 |
                                                SecurityProtocolType.Tls12 |
                                                SecurityProtocolType.Tls13;
                    }

                }
    }