class LoginService
        {
            public async Task Login(string username, string password)
            {
                HttpWebRequest request = new HttpWebRequest(new Uri(String.Format("{0}Token", Constants.BaseAddress)));
                request.Method = "POST";

                string postString = String.Format("username={0}&password={1}&grant_type=password",
                HttpUtility.HtmlEncode(username), HttpUtility.HtmlEncode(password));
                byte[] bytes = Encoding.UTF8.GetBytes(postString);
                using (Stream requestStream = await request.GetRequestStreamAsync())
                {
                    requestStream.Write(bytes, 0, bytes.Length);
                }

                try
                {
                    HttpWebResponse httpResponse =  (HttpWebResponse)(await request.GetResponseAsync());
                    string json;
                    using (Stream responseStream = httpResponse.GetResponseStream())
                    {
                        json = new StreamReader(responseStream).ReadToEnd();
                    }
                    TokenResponseModel tokenResponse = JsonConvert.DeserializeObject(json);
                    return tokenResponse.AccessToken;
                }
                catch (Exception ex)
                {
                    throw new SecurityException("Bad credentials", ex);
                }
            }
        }

Application.Current.Properties ["token"] = myToken;