一個Check AD的类。from MSDN

using System;
using System.Text;
using System.Collections;
using System.DirectoryServices;

namespace FormsAuth
{
 public class LdapAuthentication
  {
   private string _path;
   private string _filterAttribute;
  
   public LdapAuthentication(string path)
   {
    _path = path;
   }
    
   public bool IsAuthenticated(string username, string pwd)
   {
   // string domainAndUsername = domain + @"\" + username;
    string domainAndUsername = username;
    DirectoryEntry entry = new DirectoryEntry(_path);
     
    try
    { 
     //Bind to the native AdsObject to force authentication.   
     object obj = entry.NativeObject;
  
     DirectorySearcher search = new DirectorySearcher(entry);
  
     search.Filter = "(SAMAccountName=" + username + ")";
     search.PropertiesToLoad.Add("cn");
     SearchResult result = search.FindOne();
  
     if(null == result)
     {
      return false;
     }
  
     //Update the new path to the user in the directory.
     _path = result.Path;
     _filterAttribute = (string)result.Properties["cn"][0];
    }
    catch
    {
     //throw new Exception("Error authenticating user. " + ex.Message);
     return false;
    }
  
    return true;
   }
  
   public string GetGroups()
   {
   // string _path=_path;
    DirectorySearcher search = new DirectorySearcher(_path);
    search.Filter = "(cn=" + _filterAttribute + ")";
    search.PropertiesToLoad.Add("memberOf");
    StringBuilder groupNames = new StringBuilder();
  
    try
    {
     SearchResult result = search.FindOne();
     int propertyCount = result.Properties["memberOf"].Count;
     string dn;
     int equalsIndex, commaIndex;
      
     for(int propertyCounter = 0; propertyCounter < propertyCount; propertyCounter++)
     {
      dn = (string)result.Properties["memberOf"][propertyCounter];
      equalsIndex = dn.IndexOf("=", 1);
      commaIndex = dn.IndexOf(",", 1);
      if(-1 == equalsIndex)
      {
       return null;
      }
      groupNames.Append(dn.Substring((equalsIndex + 1), (commaIndex - equalsIndex) - 1));
      groupNames.Append("|");
     }
    }
    catch(Exception ex)
    {
    
     throw new Exception("Error obtaining group names. " + ex.Message);
    }   
    return groupNames.ToString();
   }
  }
}