minor #17444 Adding info about when the firewall needs to encompass all pages (ThomasLandauer)

This PR was merged into the 5.4 branch.

Discussion
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Adding info about when the firewall needs to encompass all pages

Added benefit: This also makes clear right away, that if somebody has multiple ways to login, the solution is not multiple firewalls, but one firewall (and a chain user provider).

Commits
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06c0809 Adding info about when the firewall needs to encompass all pages

Author: javiereguiluz

security.rst

@@ -576,15 +576,13 @@ will be able to authenticate (e.g. login form, API token, etc).
 Only one firewall is active on each request: Symfony uses the ``pattern`` key
 to find the first match (you can also
 :doc:`match by host or other things </security/firewall_restriction>`).
+Here, all "real" URLs are handled by the ``main`` firewall (no ``pattern`` key means
+it matches *all* URLs). 
 
 The ``dev`` firewall is really a fake firewall: it makes sure that you
 don't accidentally block Symfony's dev tools - which live under URLs like
 ``/_profiler`` and ``/_wdt``.
 
-All *real* URLs are handled by the ``main`` firewall (no ``pattern`` key means
-it matches *all* URLs). A firewall can have many modes of authentication,
-in other words, it enables many ways to ask the question "Who are you?".
-
 Often, the user is unknown (i.e. not logged in) when they first visit your
 website. If you visit your homepage right now, you *will* have access and
 you'll see that you're visiting a page behind the firewall in the toolbar:
@@ -594,7 +592,14 @@ you'll see that you're visiting a page behind the firewall in the toolbar:
 
 Visiting a URL under a firewall doesn't necessarily require you to be authenticated
 (e.g. the login form has to be accessible or some parts of your application
-are public). You'll learn how to restrict access to URLs, controllers or
+are public). On the other hand, all pages that you want to be *aware* of a logged in
+user have to be under the same firewall. So if you want to display a "You are logged in
+as ..." message on every page, they all have to be included in the same firewall.
+
+The same firewall can have many modes of authentication,
+in other words, it enables many ways to ask the question "Who are you?".
+
+You'll learn how to restrict access to URLs, controllers or
 anything else within your firewall in the :ref:`access control
 <security-access-control>` section.