// AppController.php
public $components = array(
    'Session',
    'Auth' => array(
        'authenticate' => array(
            'Blowfish' => array(
                'scope' => array('User.is_active' => true)
            )
        ),
        'loginRedirect' => array('controller' => 'pages', 'action' => 'home'),
        'logoutRedirect' => array('controller' => 'pages', 'action' => 'home')
     )
);

// UsersController.php
public function login() {
    if($this->request->is('post')) {
        if($this->Auth->login()) {
            $this->redirect($this->Auth->redirect());
        } else {
            $this->Session->setFlash('Invalid username or password, try again.');
        }
    }
}