Please note: I have revised this article to become part of the official documentation of the Security Component.

The Security Context

Central to the Security Component is the security context, which is an instance of SecurityContext. When all steps in the process of authenticating the user have been taken successfully, the security context may be asked if the authenticated user has access to a certain action or resource of the application.

use Symfony\Component\Security\SecurityContext;
use Symfony\Component\Security\Core\Exception\AccessDeniedException;

$context = new SecurityContext();

// authenticate the user...

if (!$context->isGranted('ROLE_ADMIN')) {
    throw new AccessDeniedException();
}

A firewall for HTTP requests

Authenticating a user is done by the firewall. An application may have multiple secured areas, so the firewall is configured using a map of these secured areas. For each of these areas, the map contains a request matcher and a collection of listeners. The request matcher gives the firewall the ability to find out if the current request points to a secured area. The listeners are then asked if the current request can be used to authenticate the user.

In the Symfony2 security documentation both the firewalls and the access control rules are demonstrated using the “path” option, which is used to determine if a firewall or rule is applicable to the current URL. Also the “ip” option is demonstrated. The fact of the matter is, the string based configuration options in security.yml are transformed into objects of class RequestMatcher. This is a curious class in the HttpFoundation component which allows you to match a given Request object. The Security component uses it to determine if it should activate a certain firewall for the current request (usually only by checking the request’s path info).