How to use LDAP in asp.net c#

public bool IsAuthenticated(string domain, string username, string pwd)
  {
    string domainAndUsername = domain + @"\" + username;
    DirectoryEntry entry = new DirectoryEntry(_path, domainAndUsername, pwd);

    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 (Exception ex)
    {
      throw new Exception("Error authenticating user. " + ex.Message);
    }

    return true;
  }