使用 WebClient 时出现 System.Net.WebException：无法创建 SSL/TLS 安全通道

Question

当我执行以下代码时

System.Net.ServicePointManager.ServerCertificateValidationCallback = (sender, certificate, chain, errors) => {
    return true;
};
var webClient = new WebClient();
var s = webClient.DownloadString("https://jtlplugins.x-volution.de/api.php?apikey=yS5VS7OiG1ukiIqLzCSYuFCjeF1qSskKOQeCtVxh&do=pruefe_app&cappid=123&chardwareid=DC0D-BFEA-6F79-58DE-21E9-BA3A-B288-C46F&clizenzschluessel=123");

我总是收到 System.Net.WebException：无法创建 SSL/TLS 安全通道

当我执行此操作时

https://jtlplugins.x-volution.de/api.php?apikey=yS5VS7OiG1ukiIqLzCSYuFCjeF1qSskKOQeCtVxh&do=pruefe_app&cappid=123&chardwareid=DC0D-BFEA-6F79-58DE-21E9-BA3A-B288-C46F&clizenzschluessel=123

例如直接在 Firefox 或 Internet Explorer 中，它可以工作并返回结果。

如果我的代码也像在浏览器中一样执行，我该怎么办？

我已阅读 stackoverflow 中有关此问题的其他帖子 - 但它们并没有解决我的问题 :-(

Answer 1

下面是一个继承的 WebClient 类，它解决了很多像这样的一般问题......

using System;
using System.Net;
namespace YourProgram.Web
{
    public class WebClient : System.Net.WebClient
    {
        public WebClient()
        {
            ServicePointManager.Expect100Continue = true;
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
            ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };
            this.container = new CookieContainer();
        }
        public WebClient(CookieContainer container)
        {
            this.container = container;
        }

        public CookieContainer CookieContainer
        {
            get { return container; }
            set { container = value; }
        }

        private CookieContainer container = new CookieContainer();

        protected override WebRequest GetWebRequest(Uri address)
        {
            WebRequest r = base.GetWebRequest(address);
            var request = r as HttpWebRequest;
            if (request != null)
            {
                request.CookieContainer = container;
            }
            return r;
        }

        protected override WebResponse GetWebResponse(WebRequest request, IAsyncResult result)
        {
            WebResponse response = base.GetWebResponse(request, result);
            ReadCookies(response);
            return response;
        }

        protected override WebResponse GetWebResponse(WebRequest request)
        {
            WebResponse response = base.GetWebResponse(request);
            ReadCookies(response);
            return response;
        }

        private void ReadCookies(WebResponse r)
        {
            var response = r as HttpWebResponse;
            if (response != null)
            {
                CookieCollection cookies = response.Cookies;
                container.Add(cookies);
            }
        }
    }
}

享受...

Answer 2

如果你关闭 fiddler（如果你已经打开它）并添加以下异常应该会消失

ServicePointManager.Expect100Continue = true;                
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

或者至少当我像这样尝试你的代码时它对我有用

try
{
     ServicePointManager.Expect100Continue = true;                
     ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

     ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };

     var webClient = new WebClient();

     var s = webClient.DownloadString("https://jtlplugins.x-volution.de/api.php?apikey=yS5VS7OiG1ukiIqLzCSYuFCjeF1qSskKOQeCtVxh&do=pruefe_app&cappid=123&chardwareid=DC0D-BFEA-6F79-58DE-21E9-BA3A-B288-C46F&clizenzschluessel=123");

     MessageBox.Show("Result" + s);
}
catch(Exception ex)
{ 
  MessageBox.Show(ex.Message); 
}

• 不安全的代码警告 - 尽管我假设您已经知道这一点并且不是您的代码收到 WebException 的原因，但在最初发布此问题后的几十年内，我仍向潜在的未来读者添加警告。代码：

  System.Net.ServicePointManager.ServerCertificateValidationCallback =（发件人，证书，链，错误）=> { 返回真； };

将忽略任何证书验证错误，因此根据定义并不完全安全。请看问题C# Ignore certificate errors?