1. 使用“Accept-Encoding”之前，将HttpWebRequest的属性“UnsafeAuthenticatedConnectionSharing”设置为true。这将使能设置不安全的请求头。示例代码：

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url); request.UnsafeAuthenticatedConnectionSharing = true; request.Headers["Accept-Encoding"] = "gzip, deflate";

2. 或者，您可以禁用“UnsafeAuthenticatedConnectionSharing”属性并手动设置请求头，如下所示：

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url); request.Headers["Accept-Encoding"] = "gzip, deflate"; request.ServicePoint.Expect100Continue = false; ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12; using (HttpWebResponse response = (HttpWebResponse)request.GetResponse()) { // handle response }