.Net C#域账号登陆验证

//获取登陆页输入的域账号、密码
string domainIP = "";　　　　　　//域IP
string userAccount = "";　　　　//域账号
string Password = "";　　　　　　//域账号密码 　　　　　　　　　
using (DirectoryEntry deUser = new DirectoryEntry(@"LDAP://" + domainIP, userAccount, Password))
{
DirectorySearcher src = new DirectorySearcher(deUser);
src.Filter = "(&(&(objectCategory=person)(objectClass=user))(sAMAccountName=" + userAccount + "))";
src.PropertiesToLoad.Add("cn");
src.SearchRoot = deUser;
src.SearchScope = SearchScope.Subtree;

SearchResult result = src.FindOne();
if (result != null)//验证成功
{
DirectoryEntry de = result.GetDirectoryEntry();
string userID = de.Username;
#region 域账号验证通过后判断是否用户在本系统中
var existUser = new DAL.Maintain.UserOP().GetData(userID);
if (existUser == null)
{
ViewBag.ErrorInfo = "提示：您未开通系统的权限，请联系管理员。
You have no access to the system, please contact the administrator!";
return View();
} 
#endregion

FormsAuthentication.SetAuthCookie(userID, false);
Session.Add("UserID", userID);
Logger.DefaultLog.Info("登陆sessionUserID:" + Session["UserID"].ToString());

if (string.IsNullOrEmpty(ReturnUrl))
{
return Redirect(Url.Action("Index", "Home"));
}
else
{
//...
}
}
else
{
ViewBag.ErrorInfo = "提示：登录失败: 未知的用户名或错误密码。
Account or Password is incorrect!";
return View();
}

}