autenticação no active directory utilizando login windows

function LoginAD(pDominio, pUsuario, pSenha: String): Boolean; 
var 
  Adc_Login: TADOConnection; 
  Qry_Login: TADOQuery; 
begin            
  if Trim(pSenha) <> '' then 
  begin 
    Adc_Login:= TADOConnection.Create(Application); 
    Qry_Login:= TADOQuery.Create(Adc_Login); 
    Qry_Login.Connection := Adc_Login; 

    Adc_Login.LoginPrompt := False; 
    Adc_Login.KeepConnection := False; 
    Adc_Login.Mode := cmRead; 
    Adc_Login.Provider := 'AdsDSOObject'; 

    Result := True; 
    try 
      //Passa o Dominio, usuário e senha do LDAP na string de conexão... 
      Qry_Login.SQL.Text := 
        ' SELECT' + 
        '   cn' + 
        ' FROM' + 
        '   %Dominio%' + 
        ' WHERE objectClass = ''cn'' '; 
      Qry_Login.CursorType := ctStatic; 

      Qry_Login.Close; 


      Adc_Login.ConnectionString := 
        'Provider=ADsDSOObject;Encrypt Password=True;Data Source=LDAP://' + pDominio + 
        ';User ID =' + pUsuario + 
        ';Password=' + pSenha + 
        ';Mode=Read'; 
      Adc_Login.Open; 
      Adc_Login.Connected := True; 

      try 
        with (Qry_Login) do 
        begin 
          Close; 
          SQL.Text := StringReplace(SQL.Text, '%Dominio%', QuotedStr('LDAP://'+pDominio), [rfReplaceAll]); 
          Mensagem(SQL.Text); 
          Open; 
        end; 
      except 
        Result := False; 
      end; 
    finally 
      FreeAndNil(Qry_Login); 
      FreeAndNil(Adc_Login); 
    end; 
  end 
    else 
      Result := False; 
end;