试试这个代码

using (var client = new HttpClient())
  {
      try
      {

          String url = "https://www.example-http-request.com/json";

          var httpClient = new HttpClient(new HttpClientHandler());
          var values = new List<KeyValuePair<string, string>>
          {
              new KeyValuePair<string, string>("Authorization", acesstoken)
          };
          HttpResponseMessage response = await httpClient.PostAsync(new Uri(url), new FormUrlEncodedContent(values));
          response.EnsureSuccessStatusCode();
          var responsesStr = await response.Content.ReadAsStringAsync();
          if (!responsesStr.Equals(""))
          {

              //http request data now capture in responseToken string.
              //you can change name as per your requirement.

              String responseOutput = responsesStr;


              //now convert/parse your json using Newtonsoft JSON library
              // Newtonsoft JSON Librar link : { http://james.newtonking.com/json }

                 //LoggingModel is a class which is the model of deserializing your json output.
                 LoggingModel array = JsonConvert.DeserializeObject<LoggingModel>(responseOutput);

                  bool isSuccess = array.IsSuccessful;

                  if (isSuccess == true)
                  {
                      //if success

                  }else{

                      //if login failed

                  }


            }else{

                  //no response in http request failed.                                    
            }  
      }
      catch (Exception ex)
      {
          //catch exceptio here
      }
}