How to get ip address of client machine if connected with VPN outside the company domain

private string GetPublicIpAddress()
  {
      var request = (HttpWebRequest)WebRequest.Create("http://ifconfig.me");

      request.UserAgent = "curl"; // this simulate curl linux command

      string publicIPAddress;

      request.Method = "GET";
      using (WebResponse response = request.GetResponse())
      {
          using (var reader = new StreamReader(response.GetResponseStream()))
          {
              publicIPAddress = reader.ReadToEnd();
          }
      }

      return publicIPAddress.Replace("\n", "");
  }