Policies¶

Creating Policies¶

You can create policies in your src/Policy directory. Policy classes don’t have a common base class or interface they are expected to implement. Application classes are then ‘resolved’ to a matching policy class. See the Policy Resolvers section for how policies can be resolved.

Generally you’ll want to put your policies in src/Policy and use the Policy class suffix. For now we’ll create a policy class for the Article entity in our application. In src/Policy/ArticlePolicy.php put the following content:

<?php
namespace App\Policy;

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

class ArticlePolicy
{
}

In addition to entities, table objects and queries can have policies resolved. Query objects will have their repository() method called, and a policy class will be generated based on the table name. A table class of App\Model\Table\ArticlesTable will map to App\Policy\ArticlesTablePolicy.

You can generate empty policy classes for ORM objects using bake:

# Create an entity policy
bin/cake bake policy --type entity Article

# Create a table policy
bin/cake bake policy --type table Articles

Writing Policy Methods¶

The policy class we just created doesn’t do much right now. Lets define a method that allows us to check if a user can update an article:

public function canUpdate(IdentityInterface $user, Article $article)
{
    return $user->id == $article->user_id;
}

Policy methods must return true or a Result objects to indicate success. All other values will be interpreted as failure.

Policy methods will receive null for the $user parameter when handling unauthencticated users. If you want to automatically fail policy methods for anonymous users you can use the IdentityInterface typehint.

Policy Result Objects¶

In addition to booleans, policy methods can return a Result object. Result objects allow more context to be provided on why the policy passed/failed:

use Authorization\Policy\Result;

public function canUpdate(IdentityInterface $user, Article $article)
{
    if ($user->id == $article->user_id) {
        return new Result(true);
    }
    // Results let you define a 'reason' for the failure.
    return new Result(false, 'not-owner');
}

Any return value that is not true or a ResultInterface object will be considered a failure.

Policy Scopes¶

In addition to policies being able to define pass/fail authorization checks, they can also define ‘scopes’. Scope methods allow you to modify another object applying authorization conditions. A perfect use case for this is restricting a list view to the current user:

namespace App\Policy;

class ArticlesTablePolicy
{
    public function scopeIndex($user, $query)
    {
        return $query->where(['Articles.user_id' => $user->getIdentifier()]);
    }
}

Policy Pre-conditions¶

In some policies you may wish to apply common checks across all operations in a policy. This is useful when you need to deny all actions to the provided resource. To use pre-conditions you need to implement the BeforePolicyInterface in your policy:

namespace App\Policy;

use Authorization\Policy\BeforePolicyInterface;

class ArticlesPolicy implements BeforePolicyInterface
{
    public function before($user, $resource, $action)
    {
        if ($user->getOriginalData()->is_admin) {
            return true;
        }
        // fall through
    }
}

Before hooks are expected to return one of three values:

• true The user is allowed to proceed with the action.

• false The user is not allowed to proceed with the action.

• null The before hook did not make a decision, and the authorization method will be invoked.

Scope Pre-conditions¶

Like policies, scopes can also define pre-conditions. These are useful when you want to apply common conditions to all scopes in a policy. To use pre-conditions on scopes you need to implement the BeforeScopeInterface in your scope policy:

namespace App\Policy;

use Authorization\Policy\BeforeScopeInterface;

class ArticlesTablePolicy implements BeforeScopeInterface
{
    public function beforeScope($user, $query, $action)
    {
        if ($user->getOriginalData()->is_trial_user) {
            return $query->where(['Articles.is_paid_only' => false]);
        }
        // fall through
    }
}

Before scope hooks are expected to return the modified resource object, or if null is returned then the scope method will be invoked as normal.