通知的保持活动连接C#

每当从网站获取的文本（需要POST方法登录）发生更改时，我都需要在用户的dekstop上显示通知。该网站有一个包含可由管理员编辑的文本的表，因此包含HTML页面源的字符串会发生更改。我认为连接应该始终处于活动状态，以便提供实时通知。我已经有了登录网站的代码，但当方法结束时，连接就会关闭。

我的问题是：归档保持连接并在桌面上显示通知的最佳方式是什么？

这是登录代码：

public async static Task<string> LoginAsync(string reqUri, string postData)
    {
        // Create a request using a URL that can receive a post. 
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(reqUri);
        // Set the Method property of the request to POST.
        request.Method = "POST";
        // Set the ContentType property of the WebRequest.
        request.ContentType = "application/x-www-form-urlencoded";
        // Convert POST data to a byte array.
        byte[] data = Encoding.UTF8.GetBytes(postData);
        // Get request stream and write data to it
        using (var requestStream = await Task<Stream>.Factory.FromAsync(request.BeginGetRequestStream, request.EndGetRequestStream, null))
        {
            await requestStream.WriteAsync(data, 0, data.Length);
        }
        return await GetResponse(request);
    }

    private async static Task<string> GetResponse(HttpWebRequest request)
    {
        string _response = null;
        // Get response from the website
        using (var response = (HttpWebResponse)(await Task<WebResponse>.Factory.FromAsync(request.BeginGetResponse, request.EndGetResponse, null)))
        {
            // Get the response stream
            using (Stream responseStream = response.GetResponseStream())
            {
                using (StreamReader sr = new StreamReader(responseStream, Encoding.GetEncoding("iso-8859-1")))
                {
                    // Get the response string from the website
                    _response = await sr.ReadToEndAsync();
                }
            }
        }
        return _response;
    }