minor symfony#6740 Add little comment indicating meaning of $firewall variable (ruslan-fidesio, WouterJ)

This PR was merged into the 2.7 branch.

Discussion
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Add little comment indicating meaning of $firewall variable

Finishes symfony#5981

Commits
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2a702c3 Improve comment
2545203 If context is defined, it is used instead of the firewall

Author: wouterj

cookbook/testing/simulating_authentication.rst

@@ -9,8 +9,7 @@ It could become an issue especially when ``form_login`` is used, since
 it requires additional requests to fill in and submit the form.
 
 One of the solutions is to configure your firewall to use ``http_basic`` in
-the test environment as explained in
-:doc:`/cookbook/testing/http_authentication`.
+the test environment as explained in :doc:`/cookbook/testing/http_authentication`.
 Another way would be to create a token yourself and store it in a session.
 While doing this, you have to make sure that an appropriate cookie is sent
 with a request. The following example demonstrates this technique::
@@ -45,7 +44,9 @@ with a request. The following example demonstrates this technique::
         {
             $session = $this->client->getContainer()->get('session');
 
+            // the firewall context (defaults to the firewall name)
             $firewall = 'secured_area';
+
             $token = new UsernamePasswordToken('admin', null, $firewall, array('ROLE_ADMIN'));
             $session->set('_security_'.$firewall, serialize($token));
             $session->save();