Basic Auth in CakePHP on json request

AppController.php

class AppController extends Controller
{

    public $components = array(
        'RequestHandler',
        'Auth',
    );

    public function beforeFilter() {
        $this->__setupAuth();
    }

    protected function __setupAuth() {
        $this->Auth->authenticate = array(
            AuthComponent::ALL => array(
                'fields' => array(
                    'username' => 'email',
                    'password' => 'password'
                ),
            ),
            'Form',
        );

        if (isset($this->request->params['ext']) && $this->request->params['ext'] == 'json') {
            $this->Auth->authenticate = array('Basic');
            if (!$this->Auth->login()) {
                $data = array (
                    'status' => 400,
                    'message' => $this->Auth->authError,
                );
                $this->set('data', $data);
                $this->set('_serialize', 'data');

                $this->viewClass = 'Json';
                $this->render();
            }
        }
    }

}