Code

 namespace CuteChat.WinAuthLib
{
 using System;
 using System.Collections;
 using System.Collections.Specialized;
 using System.Configuration;
 using System.Data;
 using System.Data.SqlClient;

 using System.DirectoryServices;

 using CuteChat;
 using CuteChat.SqlServer;
 
 public class WinAuthDataProvider : SqlDataProvider
 {
  public WinAuthDataProvider(string connectionstring):base(connectionstring)
  {
  }

  private DirectoryEntry OpenPath()
  {
   NameValueCollection appSettings=ConfigurationSettings.AppSettings;

   //WinNT: case sensitive
   //"WinNT://." , WinNT://DOMAIN/SERVER , WinNT://WORKGROUP/PCNAME
   
   string path=appSettings["WinAuthPath"];
   
   string username=appSettings["WinAuthUsername"];
   string password=appSettings["WinAuthPassword"];
   
   if(path==null)path="WinNT://.";//local

   if(username==null)
    return new DirectoryEntry(path);

   return new DirectoryEntry(path,username,password);
  }

  public override string[] ListUserUniqueName()
  {
   ArrayList names=new ArrayList();

   using(DirectoryEntry nt=OpenPath())
   {
    foreach(DirectoryEntry child in nt.Children)
    {
     if(child.SchemaClassName=="User")
     {
      names.Add(child.Properties["Name"].Value);
     }
    }
   }

   return (string[])names.ToArray(typeof(string));
  }

  public override UserInfoData GetUserInfo(string useruniquename)
  {
   using(DirectoryEntry nt=OpenPath())
   {
    foreach(DirectoryEntry child in nt.Children)
    {
     if(child.SchemaClassName=="User")
     {
      string name=Convert.ToString(child.Properties["Name"].Value);
      if(string.Compare(name,useruniquename,true)==0)
      {
       bool isadmin=string.Compare(useruniquename,ConfigurationSettings.AppSettings["AdminLoginName"],true)==0;

       string fullname=Convert.ToString(child.Properties["FullName"].Value);
       if(fullname==null||fullname.Length==0)
        fullname=name;

       return new UserInfoData(useruniquename,fullname,isadmin);
      }
     }
    }
   }
   throw(new Exception("User not found"));
  }

  public override bool IsUserNickNameExists(string nickname)
  {
   using(DirectoryEntry nt=OpenPath())
   {
    foreach(DirectoryEntry child in nt.Children)
    {
     if(child.SchemaClassName=="User")
     {
      string name=Convert.ToString(child.Properties["Name"].Value);
      string full=Convert.ToString(child.Properties["FullName"].Value);
      if(string.Compare(name,nickname,true)==0)
       return true;
      if(string.Compare(full,nickname,true)==0)
       return true;
     }
    }
   }
   return false;
  }

 }
}