private async Task <OAuthToken> Send(HttpPropertyList parameters)
        {
            OAuthToken token = null;

            try
            {
                string body    = parameters.FormEncode();
                string request = await new HttpHelper(_settings.EndPoint)
                                 .SendRequest(HttpMethod.Post, "/oauth/access_token", body, null, "application/x-www-form-urlencoded");

                token = OAuthToken.ParseJson(request);
            }
            catch (InvalidResponseException ex)
            {
                if (ex.InvalidResponseEntity.BadRequest == "invalid_client")
                {
                    OnAuthorizationFailed();
                }
                throw;
            }

            return(token);
        }