Keep-Alive connection for notifications C#

Question

I need to show a notification on the user's dekstop whenever the text taken from a website (that requires POST method to login) changes. The website has a table with text that can be edited by the admin, so the string containing the HTML page source changes. I think that the connection should be always active in order to provide real-time notification. I already have the code to perform the login to the website, but the connection closes when the method ends.

My problem is: what's the best way to archive keep-alive connection and show a notification on the desktop?

Here's the login code:

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;
    }

Answer 1

The best approach is to use SignalR, not HTTP. If you don't control the server and SignalR isn't available, then you'll need to just poll on some interval.