auth

<?php

class AuthHelper extends Zend_Controller_Action_Helper_Abstract {

    // controller action helpers can be hooked into the dispatch process which is what we need here
    public function preDispatch()
    {
        $controller = this->getActionController();
        if ($controller instanceof NewAuthenticable) {
            $this->auth();
        }
    }

    private auth()
    {
        //...
    }
}

// marker interface
interface NewAuthenticable
{

}

class MyController extends Zend_Rest_Controller implements NewAuthenticable
{

}

// registering is like this
class Bootstrap extends Zend_Application_Bootstrap_Bootstrap
{
    protected function _initAuthHelper()
    {
        Zend_Controller_Action_HelperBroker::addHelper(
            new AuthHelper()
        );
    }
}