title: C# HttpClient Digest Authentication not work
body: <p>I have .NET Standard 2.1 library to communicate with HTTP API with digest authentication. 
  Here is C# code:</p>
  
  <pre><code>var credCache = new CredentialCache
  {
      {
          new Uri($"http://192.168.13.100/"),
          "Digest",
          new NetworkCredential("admin", "admin")
      }
  };
  
  var httpClientHandler = new HttpClientHandler
  {
      PreAuthenticate = true,
      Credentials = credCache
  };
  httpClient = new HttpClient(httpClientHandler);
  
  SendSMS sendSms = new SendSMS()
  {
      text = message,
      param = new SendSMSParam[1] {
          new SendSMSParam()
          {
              number = phone,
              user_id = messageId
          }
      },
      port = new int[1] { port },
      encoding = "unicode",
      request_status_report = true,
  };
  
  string json = JsonConvert.SerializeObject(sendSms);
  
  HttpResponseMessage response = await httpClient.PostAsync("http://192.168.13.100/api/send_sms", new StringContent(json));
  string answer = await response.Content.ReadAsStringAsync();
  </code></pre>
  
  <p>The problem is that answer from first request is:</p>
  
  <p>HTTP/1.1 401 Unauthorized
  Server: Web Server/2.1.0 PeerSec-MatrixSSL/3.9.5-OPEN
  Date: Wed Jun  3 14:04:34 2020
  WWW-Authenticate: Digest realm="Web Server", domain="",qop="auth", nonce="7d65e9cdaa4eea9a6b12d10bda58269a", opaque="5ccc069c403ebaf9f0171e9517f40e41",algorithm="MD5", stale="FALSE"
  Set-Cookie: devckie=db39-a230-9038-0160;path=/
  Pragma: no-cache
  Cache-Control: no-cache
  Content-Type: text/html</p>
  
  <p>Document Error: Unauthorized
  Access Error: Unauthorized
  Access to this document requires a User ID</p>
  
  <p>The httpclient have to make second request with proper authorization but second request is not send. I search for solution about two days without success. Does someone know solution about this problem. T try solution from this question:<a href="https://stackoverflow.com/questions/59939357/net-core-httpclient-digest-authentication">.Net Core HttpClient Digest Authentication</a> but not work for me. The HTTP API works correctly with POSTMAN and web browser(Firefox, Edge etc.).</p>