AppController.php

<?php
App::uses('Controller', 'Controller');

class AppController extends Controller {
  public $components = array('Session', 'Auth');

  public function isPrefix($prefix) {
    return isset($this->request->params['prefix']) && $this->request->params['prefix'] == $prefix;
  }

  public function beforeFilter() {
    $this->Auth->authenticate = array('Form' => array(
      'userModel' => 'Funcionario',
      'fields'  => array(
        'username' => 'nome',
        'password' => 'senha'
      )
    ));

    $this->Auth->loginAction = array(
      'controller' => 'funcionarios',
      'action'     => 'login',
      'admin'      => false
    );

    if ($this->action == 'login') {
      $this->layout = 'login';
    }
    
    if ($this->isPrefix('admin')) {
      $this->layout = 'admin';
    } else {
      $this->Auth->allow();
    }

    parent::beforeFilter();
  }
}