Customizing Authorization for Specific Identities

Question

How do I customize authorization for a particular identity?

Answer

The first thing you want to do is ensure you have some form of authentication configured so that an identity other than "guest" will be part of the system. It is also important that you have utilized and learned the limitations of the existing authorization setup.

One of the limitations of the current authorization system is that authorization is limited to granting access to users based on whether they are an unauthenticated user (which, in Apigility, goes by the identity "guest") or an authenticated user, whose identity will be stored in the ZF\MvcAuth\Identity\AuthenticatedIdentity model.

As mentioned in the advanced authentication and authorization section, there are a few things that need to be known and taken into account in order to achieve our goal:

• The AclAuthorizationFactory will produce a Zend\Permissions\Acl type of object with the information that was written to a config file, provided by the Apigility UI.

• The AuthorizationService is composed in the ZF\MvcAuth\MvcAuthEvent, which is accessible to all MvcAuth events.

• The MvcAuth::AUTHENTICATION event has a ZF\MvcAuth\Authorization\DefaultAuthorizationListener that is responsible for ultimately calling isAuthorized(), and returning this result to be used by MvcAuth or Apigility in order to determine how to respond to the client's request.

Knowing these things, the easiest solution would be to write a listener that will execute before the DefaultAuthorizationListener, and modify the AuthorizationService/ACL in order to set our own custom rules.

For the purposes of this example, we'll place our listener in the Application module:

namespace Application;

use Zend\Mvc\MvcEvent;
use Zend\Mvc\ModuleRouteListener;
use Application\Authorization\AuthorizationListener;
use ZF\MvcAuth\MvcAuthEvent;

class Module
{
    public function onBootstrap(MvcEvent $e)
    {
        $eventManager        = $e->getApplication()->getEventManager();
        $moduleRouteListener = new ModuleRouteListener();
        $moduleRouteListener->attach($eventManager);

        // Wire in our listener at priority >1 to ensure it runs before the
        // DefaultAuthorizationListener
        $eventManager->attach(
            MvcAuthEvent::EVENT_AUTHORIZATION,
            new AuthorizationListener,
            100
        );
    }
    // ...
}

Lastly, we'll need to construct our listener. Refer to the inline comments:

namespace Application\Authorization;

use ZF\MvcAuth\MvcAuthEvent;

class AuthorizationListener
{
    public function __invoke(MvcAuthEvent $mvcAuthEvent)
    {
        /** @var \ZF\MvcAuth\Authorization\AclAuthorization $authorization */
        $authorization = $mvcAuthEvent->getAuthorizationService();

        /**
         * Regardless of how our configuration is currently through via the Apigility UI,
         * we want to ensure that the default rule for the service we want to give access
         * to a particular identity has a DENY BY DEFAULT rule.  In our case, it will be
         * for our FooBar\V1\Rest\Foo\Controller's collection method GET.
         *
         * Naturally, if you have many versions, or many methods, you would want to build
         * some kind of logic to build all the possible strings, and push these into the
         * ACL. If this gets too cumbersome, writing an assertion would be the next best
         * approach.
         */
        $authorization->deny(null, 'FooBar\V1\Rest\Foo\Controller::collection', 'GET');

        /**
         * Now, add the name of the identity in question as a role to the ACL
         */
        $authorization->addRole('ralph');

        /**
         * Next, assign the particular privilege that this identity needs.
         */
        $authorization->allow('ralph', 'FooBar\V1\Rest\Foo\Controller::collection', 'GET');
    }
}

To demonstrate this particular rule in action, consider the following HTTP requests:

Make a request without passing any credentials.

GET /foo HTTP/1.1
Accept: application/json

This results in the following 403 status, containing a WWW-Authenticate header that indicates no valid credentials were provided:

HTTP/1.1 403 Forbidden
WWW-Authenticate: Basic realm="Secure API"
Content-Type: application/problem+json

{
    "type": "http://www.w3c.org/Protocols/rfc2616/rfc2616-sec10.html",
    "title": "Forbidden",
    "status": 403,
    "detail": "Forbidden"
}

Next, we'll try with the user "joe":

GET /foo HTTP/1.1
Accept: application/json
Authorization: Basic am9lOmpvZQ==

The above requests results in the following response. Even though "joe" is a valid user (which we can tell by the absence of the WWW-Authenticate header), the ACLs do not allow him access to the resource, so we still get a 403 status:

HTTP/1.1 403 Forbidden
Content-Type: application/problem+json

{
    "type": "http://www.w3c.org/Protocols/rfc2616/rfc2616-sec10.html",
    "title": "Forbidden",
    "status": 403,
    "detail": "Forbidden"
}

Finally, let's try the user "ralph":

GET /foo HTTP/1.1
Accept: application/json
Authorization: Basic cmFscGg6cmFscGg=

And at long last we have success:

HTTP/1.1 200 OK
Content-Type: application/json

{
    "foo": "bar"
}

The above examples demonstrate that you can customize the ACLs present in the application without needing to alter any logic in your RPC controllers or REST resource classes. This also means that authorization failure responses will continue to return as early as possible, before any heavy operations that your application code might invoke.