HttpClient证书回调问题解决

/// <summary>
        /// httpclient请求
        /// </summary>
        /// <param name="client"></param>
        /// <param name="url"></param>
        /// <param name="mobile"></param>
        /// <param name="content"></param>
        /// <returns></returns>
        public string HttpRequest(HttpClient client, string url, string mobile, string content)
        {
            var req = new HttpRequestMessage();
            req.Headers.Clear();
            req.Headers.Add("ContentType", "application/x-www-form-urlencoded;charset=utf-8");
            req.Method = HttpMethod.Post;
            Dictionary<string, string> paras = new Dictionary<string, string>();
            paras.Add("action", "send");
            paras.Add("account", this.config.Account.UserName);
            paras.Add("password", this.config.Account.Password);
            paras.Add("mobile", mobile);
            paras.Add("content", content);
            req.Content = new FormUrlEncodedContent(paras);
            req.RequestUri = new Uri(url);
            ServicePointManager.ServerCertificateValidationCallback = ValidateServerCertificate;
            var response = client.SendAsync(req).Result;
            try
            {
                response.EnsureSuccessStatusCode();
            }
            catch (Exception ex)
            {
                Trace.TraceError("Error:{0}", ex.Message);
                return "";
            }
            return response.Content.ReadAsStringAsync().Result;
        }
        private bool ValidateServerCertificate(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
        {
            return true;
        }