客户端recaptcha验证抛出503“服务不可用”

Question

如果我在浏览器中运行该 URL，则该 URL 有效，因此密钥和响应是正确的。但是，当我在本地运行代码时，它会引发 503 错误。有什么想法吗？

using System.Collections.Generic;
using System.Configuration;
using System.Net;
using System.Net.Http;
using System.Text;
using Newtonsoft.Json;


namespace ProjectM2.Shared
{
    public class ReCaptcha
    {
        public bool Success { get; set; }
        public List<string> ErrorCodes { get; set; }

        public static bool Validate(string encodedResponse)
        {
            if (string.IsNullOrEmpty(encodedResponse)) return false;

            var client = new System.Net.WebClient();

            var secret = ConfigurationManager.AppSettings["Google.ReCaptcha.Secret"];

            if (string.IsNullOrEmpty(secret)) return false;
            var googleReply = client.DownloadString(string.Format("https://www.google.com/recaptcha/api/siteverify?secret={0}&response={1}", secret, encodedResponse));
            var reCaptcha = JsonConvert.DeserializeObject<ReCaptcha>(googleReply);

            return reCaptcha.Success;
        }
    }
}