CMS Tutorial - Authorization

With users now able to login to our CMS, we want to apply authorization rules to ensure that each user only edits the posts they own. We’ll use the authorization plugin to do this.

Installing Authorization Plugin

Use composer to install the Auhorization Plugin:

composer require cakephp/authorization:^2.0

Load the plugin by adding the following statement to the bootstrap() method in src/Application.php:

$this->addPlugin('Authorization');

Enabling the Authorization Plugin

The Authorization plugin integrates into your application as a middleware layer and optionally a component to make checking authorization easier. First, lets apply the middleware. In src/Application.php add the following to the class imports:

use Authorization\AuthorizationService;
use Authorization\AuthorizationServiceInterface;
use Authorization\AuthorizationServiceProviderInterface;
use Authorization\Middleware\AuthorizationMiddleware;
use Authorization\Policy\OrmResolver;
use Psr\Http\Message\ResponseInterface;

Add the AuthorizationProviderInterface to the implemented interfaces on your application:

class Application extends BaseApplication
    implements AuthenticationServiceProviderInterface,
    AuthorizationServiceProviderInterface

Then add the following to your middleware() method:

// Add authorization **after** authentication
$middlewareQueue->add(new AuthorizationMiddleware($this));

The AuthorizationMiddleware will call a hook method on your application when it starts handling the request. This hook method allows your application to define the AuthorizationService it wants to use. Add the following method your src/Application.php:

public function getAuthorizationService(ServerRequestInterface $request): AuthorizationServiceInterface
{
    $resolver = new OrmResolver();

    return new AuthorizationService($resolver);
}

The OrmResolver lets the authorization plugin find policy classes for ORM entities and queries. Other resolvers can be used to find policies for other resources types.

Next, lets add the AuthorizationComponent to AppController. In src/Controller/AppController.php add the following to the initialize() method:

$this->loadComponent('Authorization.Authorization');

Lastly we’ll mark the add, login, and logout actions as not requiring authorization by adding the following to src/Controller/UsersController.php:

// In the add, login, and logout methods
$this->Authorization->skipAuthorization();

The skipAuthorization() method should be called in any controller action that should be accessible to all users even those who have not logged in yet.

Creating our First Policy

The Authorization plugin models authorization and permissions as Policy classes. These classes implement the logic to check whether or not a identity is allowed to perform an action on a given resource. Our identity is going to be our logged in user, and our resources are our ORM entities and queries. Lets use bake to generate a basic policy:

bin/cake bake policy --type entity Article

This will generate an empty policy class for our Article entity. You can find the generated policy in src/Policy/ArticlePolicy.php. Next update the policy to look like the following:

<?php
namespace App\Policy;

use App\Model\Entity\Article;
use Authorization\IdentityInterface;

class ArticlePolicy
{
    public function canAdd(IdentityInterface $user, Article $article)
    {
        // All logged in users can create articles.
        return true;
    }

    public function canEdit(IdentityInterface $user, Article $article)
    {
        // logged in users can edit their own articles.
        return $this->isAuthor($user, $article);
    }

    public function canDelete(IdentityInterface $user, Article $article)
    {
        // logged in users can delete their own articles.
        return $this->isAuthor($user, $article);
    }

    protected function isAuthor(IdentityInterface $user, Article $article)
    {
        return $article->user_id === $user->getIdentifier();
    }
}

While we’ve defined some very simple rules, you can use as complex logic as your application requires in your policies.

Checking Authorization in the ArticlesController

With our policy created we can start checking authorization in each controller action. If we forget to check or skip authorization in an controller action the Authorization plugin will raise an exception letting us know we forgot to apply authorization. In src/Controller/ArticlesController.php add the following to the add, edit and delete methods:

public function add()
{
    $article = $this->Articles->newEmptyEntity();
    $this->Authorization->authorize($article);
    // Rest of the method
}

public function edit($slug)
{
    $article = $this->Articles
        ->findBySlug($slug)
        ->contain('Tags') // load associated Tags
        ->firstOrFail();
    $this->Authorization->authorize($article);
    // Rest of the method.
}

public function delete($slug)
{
    $this->request->allowMethod(['post', 'delete']);

    $article = $this->Articles->findBySlug($slug)->firstOrFail();
    $this->Authorization->authorize($article);
    // Rest of the method.
}

The AuthorizationComponent::authorize() method will use the current controller action name to generate the policy method to call. If you’d like to call a different policy method you can call authorize with the operation name:

$this->Authorization->authorize($article, 'update');

Lastly add the following to the tags, view, and index methods on the ArticlesController:

// View, index and tags actions are public methods
// and don't require authorization checks.
$this->Authorization->skipAuthorization();

Fixing the Add & Edit Actions

While we’ve blocked access to the edit action, we’re still open to users changing the user_id attribute of articles during edit. We will solve these problems next. First up is the add action.

When creating articles, we want to fix the user_id to be the currently logged in user. Replace your add action with the following:

// in src/Controller/ArticlesController.php

public function add()
{
    $article = $this->Articles->newEmptyEntity();
    $this->Authorization->authorize($article);

    if ($this->request->is('post')) {
        $article = $this->Articles->patchEntity($article, $this->request->getData());

        // Changed: Set the user_id from the current user.
        $article->user_id = $this->request->getAttribute('identity')->getIdentifier();

        if ($this->Articles->save($article)) {
            $this->Flash->success(__('Your article has been saved.'));
            return $this->redirect(['action' => 'index']);
        }
        $this->Flash->error(__('Unable to add your article.'));
    }
    $tags = $this->Articles->Tags->find('list');
    $this->set(compact('article', 'tags'));
}

Next we’ll update the edit action. Replace the edit method with the following:

// in src/Controller/ArticlesController.php

public function edit($slug)
{
    $article = $this->Articles
        ->findBySlug($slug)
        ->contain('Tags') // load associated Tags
        ->firstOrFail();
    $this->Authorization->authorize($article);

    if ($this->request->is(['post', 'put'])) {
        $this->Articles->patchEntity($article, $this->request->getData(), [
            // Added: Disable modification of user_id.
            'accessibleFields' => ['user_id' => false]
        ]);
        if ($this->Articles->save($article)) {
            $this->Flash->success(__('Your article has been updated.'));
            return $this->redirect(['action' => 'index']);
        }
        $this->Flash->error(__('Unable to update your article.'));
    }
    $tags = $this->Articles->Tags->find('list');
    $this->set(compact('article', 'tags'));
}

Here we’re modifying which properties can be mass-assigned, via the options for patchEntity(). See the Changing Accessible Fields section for more information. Remember to remove the user_id control from templates/Articles/edit.php as we no longer need it.

Wrapping Up

We’ve built a simple CMS application that allows users to login, post articles, tag them, explore posted articles by tag, and applied basic access control to articles. We’ve also added some nice UX improvements by leveraging the FormHelper and ORM capabilities.

Thank you for taking the time to explore CakePHP. Next, you should learn more about the Database Access & ORM, or you peruse the Using CakePHP.