C# HttpRequest: Not found error

I have this code:

 HttpWebRequest spAuthReq = HttpWebRequest.Create(new Uri(myURL, UriKind.RelativeOrAbsolute)) as HttpWebRequest;
 spAuthReq.Method = "GET";
 spAuthReq.BeginGetResponse(new AsyncCallback(GetResponsetStreamCallback), spAuthReq);

void GetResponsetStreamCallback(IAsyncResult callbackResult)
    {
        try
        {
            HttpWebRequest request = (HttpWebRequest)callbackResult.AsyncState;
            HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(callbackResult);
            Stream streamResponse = response.GetResponseStream();
            StreamReader reader = new StreamReader(streamResponse);
            responseString = reader.ReadToEnd();
            streamResponse.Close();
            reader.Close();
            response.Close();
            string result = responseString;
        }
        catch (WebException ex)
        {
            responseString = ex.ToString();
        }
    }

I need to get some messages but I get error: System.Net.WebException: The remote server returned an error: NotFound. Also I need to post token to server because it requies login, I have token but I don't know how to post token with GET method. Anyway, without token I should get response from server that I'm not logged in but I end up with exception.