带证书的post请求---HttpClient

 public static string HttpPostCert(string uri, string jsontxt)
        {
            var handler = new HttpClientHandler();
            handler.ClientCertificateOptions = ClientCertificateOption.Manual;
            handler.SslProtocols = SslProtocols.Tls12;
            handler.ClientCertificates.Add(new X509Certificate2("证书地址跟密码地址"));
            var retData = string.Empty;
            using (var httpClient = new HttpClient())
            {
                var content = new StringContent(jsontxt);
                content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
                var response = httpClient.PostAsync(ServiceDomain + uri, content).Result;
                retData = response.Content.ReadAsStringAsync().Result;
            }
            return retData;
        }