[#5015] Updating the security service name for 2.6 - thanks to Cordoval

Author: weaverryan

Diff for: cookbook/security/impersonating_user.rst

@@ -92,10 +92,10 @@ over the user's roles until you find one that a ``SwitchUserRole`` object::
 
     use Symfony\Component\Security\Core\Role\SwitchUserRole;
 
-    $securityContext = $this->get('security.context');
+    $authChecker = $this->get('security.authorization_checker');
 
-    if ($securityContext->isGranted('ROLE_PREVIOUS_ADMIN')) {
-        foreach ($securityContext->getToken()->getRoles() as $role) {
+    if ($authChecker->isGranted('ROLE_PREVIOUS_ADMIN')) {
+        foreach ($authChecker->getToken()->getRoles() as $role) {
             if ($role instanceof SwitchUserRole) {
                 $impersonatingUser = $role->getSource()->getUser();
                 break;