.net中,如何获得活动目录(AD)上的密码失效时间?

      据我所知,在.net没有方法直接通过获取属性的方法获得AD上密码失效的时间.要通过用户属性pwdLastSet(密码最后设置时间)和域属性maxPwdAge(密码最大寿命)这两个属性值计算获得.

pwdLastSet属性值可以通过如下代码获得,但是怎么获得maxPwdAge这个属性值,请高手相助?

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.Runtime.InteropServices;
using System.DirectoryServices;
namespace expiredate
{
    /**//// 

    /// WebForm1 的摘要说明。
    /// 

    ///ActiveDs.tlb
    public class WebForm1 : System.Web.UI.Page
    {        
        protected System.Web.UI.WebControls.TextBox TextBox1;
        protected System.Web.UI.WebControls.TextBox TextBox2;
        protected System.Web.UI.WebControls.TextBox TextBox3;
        protected System.Web.UI.WebControls.Button Button1;
        [ComImport]
        [Guid("9068270B-0939-11D1-8BE1-00C04FD8D503")]
        [InterfaceType(ComInterfaceType.InterfaceIsDual)]
        internal interface IADsLargeInteger
        {
            [DispId(0x00000002)]
            int HighPart...{get; set;}
            [DispId(0x00000003)]
            int LowPart...{get; set;}
        }
        private void Button1_Click(object sender, System.EventArgs e)
        {
            string ADUser = "1111111111111";
            string ADPassword = "22222222";
            string ADPath="LDAP://....";    
            try
            {
                 System.DirectoryServices.DirectoryEntry mUser =
                                                                         new System.DirectoryServices.DirectoryEntry(ADPath,ADUser,ADPassword);
                 mUser.RefreshCache();
                 if(mUser.Properties.Contains("pwdLastSet"))
                        {                                           
                                  IADsLargeInteger li =(IADsLargeInteger)mUser.Properties["pwdLastSet"][0];              
                             long date = (long)li.HighPart << 32 | (uint)li.LowPart;
                             DateTime time = DateTime.FromFileTime(date);
                             this.TextBox1.Text=time.ToString();
                           }
                   }
          }
}