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CookieContainer cookies = new CookieContainer();
                        HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://api.parasut.com/oauth/token?client_id=" + parasutClientID + "&client_secret=" + parasutClientSecret + "&username=" + parasutUsername + "&password=" + parasutPassword + "&grant_type=" + parasutgrant_type + "&redirect_uri=" + parasutCallBackUrl);
                        request.CookieContainer = cookies;

                        request.Method = "POST";

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

String status = ((HttpWebResponse)response).StatusDescription;

                        Stream dataStream = response.GetResponseStream();

                        StreamReader reader = new StreamReader(dataStream);

                        string responseFromServer = reader.ReadToEnd();

var parasutModel = new JavaScriptSerializer().Deserialize<ParasutModel>(responseFromServer.Trim());

//parasutModel.access_token

Please note that all pasted data is publicly available.