当我尝试保存我的json数据时，远程服务器返回了一个未经授权的错误（401）

Question

我想将json数据发布到web服务。

以下是方法：

      public static Int32 SaveCashSale(string username, string key, CashSale cashSale)
    {
        try
        {

            // Customize URL according to geo location parameters
            var url = string.Format(cashSaleUrl, username, key);

            var httpWebRequest = (HttpWebRequest)WebRequest.Create(url);
            httpWebRequest.ContentType = "application/json";
            httpWebRequest.Method = "POST";


            using (var streamWriter = new StreamWriter(httpWebRequest.GetRequestStream()))
            {
                string jsonData = new JavaScriptSerializer().Serialize(new
                {
                    activity_date = cashSale.activity_date = DateTime.Now.ToString(),
                    added_by = cashSale.added_by,
                    amount_paid = cashSale.amount_paid,
                    balance = cashSale.balance,
                    currency = cashSale.currency,
                    customer = cashSale.customer,
                    grand_total = cashSale.grand_total,
                    modified_by = cashSale.modified_by,
                    price_type = cashSale.price_type,
                    sub_total = cashSale.sub_total,
                    total_quantity = cashSale.total_quantity,
                    workspace = cashSale.workspace,
                });

                streamWriter.Write(jsonData);
                streamWriter.Flush();
                streamWriter.Close();

                var httpResponse = (HttpWebResponse)httpWebRequest.GetResponse();

                using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
                {
                    var result = streamReader.ReadToEnd();
                }

            }

        }
        catch (WebException ex)
        {
            using (WebResponse response = ex.Response)
            {
                var httpResponse = (HttpWebResponse)response;

                using (Stream data = response.GetResponseStream())
                {
                    StreamReader sr = new StreamReader(data);
                    throw new Exception(sr.ReadToEnd());
                }
            }
        }
        catch (Exception)
        {

            throw;
        }
    }

系统出现以下错误消息： 远程服务器在此行代码中返回了一个未经授权的错误（401）。：

var httpResponse = (HttpWebResponse)httpWebRequest.GetResponse();

网址格式为：

private const string ashSaleItemUrl = "http://avaris.kwekud.com/api/v1/sales/cashsale/?username={0}&api_key={1}";

我的代码有什么问题，如何解决？