Use Basic Authorization And Json Parameters.
using (HttpClient client = new HttpClient()) { var request_json = "your json string"; var content = new StringContent(request_json, Encoding.UTF8, "application/json"); var authenticationBytes = Encoding.ASCII.GetBytes("YourUsername:YourPassword"); client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", Convert.ToBase64String(authenticationBytes)); client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json")); var result = await client.PostAsync("YourURL", content); var result_string = await result.Content.ReadAsStringAsync(); }