c# httpwebrequest登录集成window身份验证的网站，有用户名和密码

[一只鬼]

这是fiddler获取到的response

HTTP/1.1 401 Unauthorized
Cache-Control: private
Content-Type: text/html
Server: Microsoft-IIS/8.5
X-AspNet-Version: 4.0.30319
Set-Cookie: .ASPXAUTH=; expires=Mon, 11-Oct-1999 16:00:00 GMT; path=/; HttpOnly
X-Frame-Options: SAMEORIGIN
Content-Security-Policy: frame-ancestors 'self'
X-Content-Type-Options: nosniff
WWW-Authenticate: Negotiate
WWW-Authenticate: NTLM
X-Powered-By: ASP.NET
P3P: CP="NON"
X-XSS-Protection: 0
Content-Length: 1181
Proxy-Support: Session-Based-Authentication
下面是我的代码

ServicePointManager.ServerCertificateValidationCallback = new System.Net.Security.RemoteCertificateValidationCallback(CheckValidationResult);//验证服务器证书回调自动验证
            HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create("url");
           
            req.PreAuthenticate = true;
            req.UseDefaultCredentials = false;
            var c = new NetworkCredential("user", "password");
            CredentialCache credentialCache = new CredentialCache();
            credentialCache.Add(new Uri("url"), "Negotiate", c);
            
            req.KeepAlive = true;
            
            req.Credentials = credentialCache;
         
            req.Method = "GET";
            req.Host = "";
            //req.ContentType = "application/x-www-form-urlencoded";
            req.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8";
            req.Headers.Add("Upgrade-Insecure-Requests", "1");
            req.UserAgent = "Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.112 Safari/537.36";
            req.Headers.Add("Cache-Control", "max-age=0");
            req.Headers.Add("Accept-Encoding", "gzip, deflate, sdch");
            req.Headers.Add("Accept-Language", "zh-CN,zh;q=0.8");
          
            HttpWebResponse res = null;


            try
            {
                res = (HttpWebResponse)req.GetResponse();
            }
            catch (WebException  er)
            {
                res = (HttpWebResponse)er.Response;
            }

返回结果一直是401，为什么？浏览器输入账号和密码就能登录进去了，网站是https的

[一只鬼]

需要把密码加密吗