Practical exemple of what can be done with a DI Container in ZF.

1-services.yml

parameters:
     auth.adapter.entityName: Application_Model_User
     auth.adapter.identityField: email
     auth.adapter.credentialField: password

services:
    auth.adapter:
        class: LoSo_Zend_Auth_Adapter_Doctrine2
        arguments: [@em, %auth.adapter.entityName%, %auth.adapter.identityField%, %auth.adapter.credentialField%]
    auth:
        class: Zend_Auth
        constructor: getInstance

2-AuthService.php

<?php 
/**
 * @Service
 */ 
class Application_Service_AuthService 
{ 
    /**
     * @var Zend_Auth
     * @Inject("auth")
     */ 
    protected $auth; 
 
    public function setAuth($auth) 
    { 
        $this->auth= $auth; 
        return $this; 
    } 
 
    /**
     * @var Application_Service_Doctrine_UserService
     * @Inject
     */ 
    protected $userService; 
 
    public function setUserService($userService) 
    { 
        $this->userService = $userService; 
        return $this; 
    } 
 
    /**
     * @var Zend_Auth_Adapter_Interface
     * @Inject("auth.adapter")
     */ 
    protected $authAdapter; 
 
    public function setAuthAdapter($authAdapter) 
    { 
        $this->authAdapter = $authAdapter; 
        return $this; 
    } 
 
    protected $user; 
 
    public function authenticate($username, $password) 
    { 
        $this->authAdapter->setIdentity($username) 
               ->setCredential($password); 
        return $this->auth->authenticate($this->authAdapter); 
    } 
 
    public function hasIdentity() 
    { 
        return $this->auth->hasIdentity(); 
    } 
 
    public function getIdentity() 
    { 
        return $this->auth->getIdentity(); 
    } 
 
    public function getIdentityAsUser() 
    { 
        if (null === $this->user) { 
            $this->user = $this->userService->findOneByEmail($this->getIdentity()); 
        } 
        return $this->user; 
    } 
 
    public function isIdentifiedUser($user) 
    { 
        return $user->getEmail() == $this->getIdentity(); 
    } 
}

3-AuthController.php

<?php
/**
 * @Service
 */
class AuthController extends LoSo_Zend_Controller_Action
{
    /**
     * @var Application_Service_Doctrine_UserService
     * @Inject
     */
    protected $userService;

    public function setUserService($userService)
    {
        $this->userService = $userService;
        return $this;
    }

    /**
     * @var Application_Service_AuthService
     * @Inject
     */
    protected $authService;

    public function setAuthService($authService)
    {
        $this->authService = $authService;
        return $this;
    }

    public function loginAction()
    {
        $loginForm = new Application_Form_Login();
        $loginForm->setAction($this->view->url(array('action' => 'authenticate')));
        $this->view->loginForm = $loginForm;
    }

    public function authenticateAction()
    {
        $loginForm = new Application_Form_Login();
        if ($this->getRequest()->isPost()) {
            if ($loginForm->isValid($_POST)) {
                $result = $this->authService->authenticate($loginForm->username->getValue(), $loginForm->password->getValue());
                if ($result->isValid()) {
                    $this->_helper->flashMessenger->setNamespace('success')->addMessage($this->view->translate('Authentication successfull.'));
                    return $this->_helper->redirector('index', 'index');
                } else {
                    switch($result->getCode()) {
                        case Zend_Auth_Result::FAILURE_CREDENTIAL_INVALID:
                            $message = 'Invalid password.';
                            break;

                        case Zend_Auth_Result::FAILURE_IDENTITY_NOT_FOUND:
                        case Zend_Auth_Result::FAILURE_IDENTITY_AMBIGUOUS:
                            $message = 'Invalid username.';
                            break;

                        default:
                            $message = 'Authentication failed.';
                    }
                    $this->_helper->flashMessenger->setNamespace('error')->addMessage($this->view->translate($message));
                    return $this->_helper->redirector('login');
                }
            } else {
                $this->view->loginForm = $loginForm;
                return $this->render('login');
            }
        }
        return $this->_helper->redirector('login');
    }

    public function logoutAction()
    {
        Zend_Auth::getInstance()->clearIdentity();
        $this->_helper->redirector('index', 'index');
    }
}