尝试使用HttpWebRequest获取身份验证cookie

HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://example.com/login");
request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";

string postData = "username=myusername&password=mypassword";
byte[] postDataBytes = Encoding.ASCII.GetBytes(postData);
request.ContentLength = postDataBytes.Length;

Stream requestStream = request.GetRequestStream();
requestStream.Write(postDataBytes, 0, postDataBytes.Length);
requestStream.Close();

HttpWebResponse response = (HttpWebResponse)request.GetResponse();
CookieCollection cookies = response.Cookies;

foreach (Cookie cookie in cookies)
{
    Console.WriteLine("Name: {0}, Value: {1}", cookie.Name, cookie.Value);
}