C#

public string[] ReceiveCookiesAndHiddenData()
        {
            string[] tempHidden = new string[4];
            HttpWebRequest tempRequest = (HttpWebRequest)WebRequest.Create(BASEURL);
            
            using (HttpWebResponse tempResponse = (HttpWebResponse)tempRequest.GetResponse()) 
            {
                HtmlDocument doc = new HtmlDocument();
                doc.Load(tempResponse.GetResponseStream());

                tempHidden[0] = doc.DocumentNode.SelectNodes("//input[@type='hidden' and @name='_sourcePage']")[0].Attributes["Value"].Value;
                tempHidden[1] = doc.DocumentNode.SelectNodes("//input[@type='hidden' and @name='__fp']")[0].Attributes["Value"].Value;
                tempHidden[2] = doc.DocumentNode.SelectNodes("//input[@type='hidden' and @name='CSRFToken']")[0].Attributes["Value"].Value;
                tempHidden[3] = tempResponse.Headers["Set-Cookie"].Split(new Char[] { ';' })[0];
            }
            return tempHidden;
        }

public void MakeActualRequest() 
        {
            hiddenData = ReceiveCookiesAndHiddenData();
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(BASEURL);
            request.Method = "POST";
            request.ContentType = "application/x-www-form-urlencoded";
            request.UserAgent = "Mozilla/5.0 (Windows NT 6.3; WOW64; rv:31.0) Gecko/20100101 Firefox/31.0";
            request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8";
            request.Referer = "https://www.regelleistung.net/ip/action/abrufwert";
            request.Headers.Add("Set-Cookie",hiddenData[3]);

            NameValueCollection outgoingQueryString = HttpUtility.ParseQueryString(String.Empty);
            outgoingQueryString.Add("von", "05.08.2014");
            outgoingQueryString.Add("uenbld", "STXs440zwks=");
            outgoingQueryString.Add("produkt", "MRL");
            outgoingQueryString.Add("work", "anzeigen");
            outgoingQueryString.Add("_sourcePage", hiddenData[0]);
            outgoingQueryString.Add("__fp", hiddenData[1]);
            outgoingQueryString.Add("CSRFToken", hiddenData[2]);
            string postdata = outgoingQueryString.ToString();

            byte[] data = Encoding.ASCII.GetBytes(postdata);
            request.ContentLength = data.Length;

            using(Stream requestStream = request.GetRequestStream())
            {
                requestStream.Write(data,0,data.Length);
            }

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();
            Stream responseStream = response.GetResponseStream();

            using(StreamReader reader = new StreamReader(responseStream, Encoding.Default))
	        {
		        string content = reader.ReadToEnd();
	        }
        }

HttpWebResponse response = (HttpWebResponse)request.GetResponse();