由于以下错误消息，我们无法使用WebRequest连接到HTTPS服务器:
请求被中止:无法创建SSL/TLS安全通道。
我们知道服务器没有有效的HTTPS证书，但为了绕过这个问题，我们使用下面的代码，我们从另一个StackOverflow帖子:
private void Somewhere() {
ServicePointManager.ServerCertificateValidationCallback += new RemoteCertificateValidationCallback(AlwaysGoodCertificate);
}
private static bool AlwaysGoodCertificate(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors policyErrors) {
return true;
}
问题是服务器从未验证证书，并出现上述错误而失败。有人知道我该怎么做吗?
我应该提到的是，我和一个同事几周前进行了测试，它运行得很好，与我上面写的类似。我们发现的唯一“主要区别”是，我用的是Windows 7，而他用的是Windows XP。这会改变什么吗?
如果服务器对HTTP请求返回HTTP 401未授权响应，则会出现“请求已终止:无法创建SSL/TLS安全通道”异常。
您可以通过打开跟踪级系统来确定是否发生这种情况。Net日志记录用于客户端应用程序，如本回答中所述。
一旦日志配置就绪，运行应用程序并重现错误，然后在日志输出中查找如下一行:
System.Net Information: 0 : [9840] Connection#62912200 - Received status line: Version=1.1, StatusCode=401, StatusDescription=Unauthorized.
在我的情况下，我未能设置服务器所期望的特定cookie，导致服务器以401错误响应请求，从而导致“无法创建SSL/TLS安全通道”异常。
在我的情况下，这个异常的根源是在代码的某些时候，下面的代码被调用:
ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3;
这真的很糟糕。它不仅指示. net使用不安全的协议，而且还会影响在您的应用域中随后发出的每一个新的WebClient(和类似的)请求。(请注意，传入的web请求在你的ASP中不受影响。NET应用程序，但新的WebClient请求，如与外部web服务对话，是)。
在我的情况下，它实际上并不需要，所以我可以删除该语句，所有其他的web请求重新开始正常工作。根据我在其他地方的阅读，我了解到一些事情:
This is a global setting in your appdomain, and if you have concurrent activity, you can't reliably set it to one value, do your action, and then set it back. Another action may take place during that small window and be impacted.
The correct setting is to leave it default. This allows .NET to continue to use whatever is the most secure default value as time goes on and you upgrade frameworks. Setting it to TLS12 (which is the most secure as of this writing) will work now but in 5 years may start causing mysterious problems.
If you really need to set a value, you should consider doing it in a separate specialized application or appdomain and find a way to talk between it and your main pool. Because it's a single global value, trying to manage it within a busy app pool will only lead to trouble. This answer: https://stackoverflow.com/a/26754917/7656 provides a possible solution by way of a custom proxy. (Note I have not personally implemented it.)
