C#： 根据url获取https的的证书有效期

using System;
using System.Net;
using System.Security.Cryptography.X509Certificates;

namespace GetServerCertificateDemo
{
    class Program3
    {
        static void Main(string[] args)
        {
            var http = new WebClient();
            var uri = new Uri("https://www.baidu.com");
            http.DownloadString(uri);
            //通过Uri获取ServicePoint
            var servicePoint = ServicePointManager.FindServicePoint(uri);
            //取服务端证书，X509Certificate格式，转一下
            var serverCert = new X509Certificate2(servicePoint.Certificate);
            Console.WriteLine("颁发给：{0}", serverCert.Subject);
            Console.WriteLine("颁发者：{0}", serverCert.Issuer);
            Console.WriteLine("序列号：{0}", serverCert.SerialNumber);
            Console.WriteLine("指  纹：{0}", serverCert.Thumbprint);
            Console.WriteLine("起  始：{0}", serverCert.NotBefore);
            Console.WriteLine("过  期：{0}", serverCert.NotAfter);
            Console.Read();
        }
    }
}