asp.Net(C#)ドメイン名サーバADアカウントの読み出し

c#  :

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

using System.Security.Principal;
using System.Runtime.InteropServices;
using System.Data.SqlClient;
using System.Web.SessionState;

public partial class login : System.Web.UI.Page
{
    String str_userId = "";
    String str_userName = "";
    String str_name = "";
    String str_email = "";
     string str_shenfen = "";

    public const int LOGON32_LOGON_INTERACTIVE = 2;
    public const int LOGON32_PROVIDER_DEFAULT = 0;
    WindowsImpersonationContext impersonationContext;
    [DllImport("advapi32.dll")]
    public static extern int LogonUserA(String lpszUserName,
    String lpszDomain,
    String lpszPassword,
    int dwLogonType,
    int dwLogonProvider,
    ref IntPtr phToken);
    [DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    public static extern int DuplicateToken(IntPtr hToken,
    int impersonationLevel, ref IntPtr hNewToken);
    [DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    public static extern bool RevertToSelf();
    [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
    public static extern bool CloseHandle(IntPtr handle);
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void btnok_Click(object sender, EventArgs e)
    {
        ///        
        if (Page.IsValid == true)
        {   ///               
            // if (impersonateValidUser(Convert.ToString(txteid.Text.Trim()), "your domain", Convert.ToString(txtpsw.Text.Trim())))
          //   {
                      IISAuthUser = Convert.ToString(txteid.Text.Trim());

            IUser user = new User();
            SqlDataReader recu = user.GetUserLoginL(IISAuthUser);
            ///        
            if (recu.Read())
            {
                str_userId = recu["UserID"].ToString();
                str_userName = recu["UserName"].ToString();
                str_name = recu["Name"].ToString();
                str_email = recu["email"].ToString();
                str_shenfen = recu["shenfen"].ToString();
               Label1.Text = "   ,   " + str_name;
            }


            recu.Close();

            ///       ，        
            if ((str_userId != null) && (str_userId != ""))
            {
                Session["UserID"] = str_userId;
                Session["UserName"] = str_userName;
                Session["Name"] = str_name;
                Session["email"] = str_email;
                Session["shenfen"] = str_shenfen;


                switch (Convert.ToString(Session["shenfen"]))
                {
                    case "staffer":
                        Session["title"] = "Fill In Purchase Order";
                        Response.Redirect("~/main.aspx?gl=apply");
                        break;
                    default:

                        Session["title"] = "Approve Purchase Order";
                        Response.Redirect("~/approve.aspx");
                        break;
                }
            }
            else
            {
                Label1.Text = "     ，   ＩＴ   ！";
            }
            //
        }
        else
        {
                      Label1.Text = "     ，   ＩＴ     ！";
        }
    //    }
    }
    private bool impersonateValidUser(String userName, String domain, String password)
    {
        WindowsIdentity tempWindowsIdentity;
        IntPtr token = IntPtr.Zero;
        IntPtr tokenDuplicate = IntPtr.Zero;
        if (RevertToSelf())
        {
            if (LogonUserA(userName, domain, password, LOGON32_LOGON_INTERACTIVE,
            LOGON32_PROVIDER_DEFAULT, ref token) != 0)
            {
                if (DuplicateToken(token, 2, ref tokenDuplicate) != 0)
                {
                    tempWindowsIdentity = new WindowsIdentity(tokenDuplicate);
                    impersonationContext = tempWindowsIdentity.Impersonate();
                    if (impersonationContext != null)
                    {
                        CloseHandle(token);
                        CloseHandle(tokenDuplicate);
                        return true;
                    }
                }
            }
        }
        if (token != IntPtr.Zero)
            CloseHandle(token);
        if (tokenDuplicate != IntPtr.Zero)
            CloseHandle(tokenDuplicate);
        return false;
    }
    private void undoImpersonation()
    {
        impersonationContext.Undo();
    }
}