请教：通过httpclient方式向doris导入数据出错“no valid Basic authorization”。username使用doris的root账号，password确认密码没错。现象是：url如果是FE的地址则会报错，而改成BE的地址则没有问题。核心代码如下：

url = $"{url}{Dbname}/{Table}/_stream_load";

byte[] postData = Encoding.UTF8.GetBytes(JsonDatas);

HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;

request.Method = "PUT";

request.KeepAlive = true;

request.AllowAutoRedirect = true;

request.ContentType = "application/json;charset=UTF-8";

request.UserAgent = "Mozilla/4.0 (compatible;MSIE 6.0;)";

request.ContentLength = postData.Length;

request.Timeout = 60000;

request.Headers.Add("expect", "100-continue");

request.Headers.Add("format", "json");

request.Headers.Add("strip_outer_array", "true");

request.Headers.Add("jsonpaths", jsonpaths);

request.Headers.Add("label", DealLabe);

request.PreAuthenticate = true;

string usernamePassword = username + ":" + password;

CredentialCache mycache = new CredentialCache();

mycache.Add(new Uri(url), "Basic", new NetworkCredential(username, password));

request.Credentials = mycache;

request.Headers.Add("Authorization", "Basic " + (Convert.ToBase64String(Encoding.UTF8.GetBytes(usernamePassword))).Cof_FilterUnVisible());

// 提交请求数据

System.IO.Stream outputStream = request.GetRequestStream();

outputStream.Write(postData, 0, postData.Length);

outputStream.Close();

HttpWebResponse response = request.GetResponse() as HttpWebResponse;

Stream responseStream = response.GetResponseStream();

StreamReader reader = new System.IO.StreamReader(responseStream, Encoding.GetEncoding("UTF-8"));

ResultStr = reader.ReadToEnd();

reader.Close();