Issue with facebook realtime API

I am using Asp.net to subscribe to facebook realtime API.I have created a Httphandler to handle http GET/POST request.

public class SubCallback : IHttpHandler {
    // This is secret verify_token that you should pass
    // to Facebook when add/modify a subscription.
    // Make sure to replace it with your own string!!
    public const string VERIFY_TOKEN = "abc";

    public void ProcessRequest (HttpContext context) {
        context.Response.ContentType = "text/plain";
        HttpRequest request = context.Request;
        if (request.HttpMethod == "GET" &&
            request.Params["hub.mode"] == "subscribe" &&
            request.Params["hub.verify_token"] == VERIFY_TOKEN)
        {
            context.Response.ContentType = "text/plain";
            context.Response.Write(request.Params["hub.challenge"]);
        }
        else if (request.HttpMethod == "POST")
        {
            StreamReader reader = new StreamReader(request.InputStream);
            string jsonString = reader.ReadToEnd();
            // Now use your favorate JSON decode and have fun with the data

        }

    }

    public bool IsReusable {
        get {
            return false;
        }
    }

I am able to subscribe to realtime API .But when i try to get the information i am getting null in content

const string VERIFY_TOKEN = "abc";
            string callbackurl = "http://somepublicurl/Default.aspx";

            string q = "?hub.mode=subscribe&&hub.verify_token=abc";
            var newt = callbackurl + q;

            HttpWebRequest request = (HttpWebRequest)
            WebRequest.Create(newt);
            HttpWebResponse response = (HttpWebResponse)
            request.GetResponse();
            Stream resStream = response.GetResponseStream();   

I am always getting resStream.Length null because request.Parms["hub.challenge"] is always null ?

Any thoughts ?