feature #5021 Explained the "Remember Me" firewall options (javiereguiluz)

This PR was merged into the 2.3 branch.

Discussion
----------

Explained the "Remember Me" firewall options

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | 2.3+
| Fixed tickets | #4193

This PR started just for adding a note about setting different cookie names for the "Remember Me" feature when using multiple firewalls ... but then I realized that the options of this important firewall weren't explained.

Commits
-------

63890b1 Put the default value alongside the name of the option to improve readability
aa91c37 Fixed a wrong explanation of the "httponly" option
7e45958 Added the (important) missing "key" option
91172bc Explained the "Remember Me" firewall options

Author: weaverryan

cookbook/security/remember_me.rst

@@ -8,10 +8,7 @@ Once a user is authenticated, their credentials are typically stored in the
 session. This means that when the session ends they will be logged out and
 have to provide their login details again next time they wish to access the
 application. You can allow users to choose to stay logged in for longer than
-the session lasts using a cookie with the ``remember_me`` firewall option.
-The firewall needs to have a secret key configured, which is used to encrypt
-the cookie's content. It also has several options with default values which
-are shown here:
+the session lasts using a cookie with the ``remember_me`` firewall option:
 
 .. configuration-block::
 
@@ -22,9 +19,8 @@ are shown here:
             main:
                 remember_me:
                     key:      "%secret%"
-                    lifetime: 31536000 # 365 days in seconds
+                    lifetime: 604800 # 1 week in seconds
                     path:     /
-                    domain:   ~ # Defaults to the current domain from $_SERVER
 
     .. code-block:: xml
 
@@ -33,9 +29,8 @@ are shown here:
             <firewall>
                 <remember-me
                     key      = "%secret%"
-                    lifetime = "31536000" <!-- 365 days in seconds -->
+                    lifetime = "604800" <!-- 1 week in seconds -->
                     path     = "/"
-                    domain   = "" <!-- Defaults to the current domain from $_SERVER -->
                 />
             </firewall>
         </config>
@@ -48,14 +43,60 @@ are shown here:
                 'main' => array(
                     'remember_me' => array(
                         'key'      => '%secret%',
-                        'lifetime' => 31536000, // 365 days in seconds
+                        'lifetime' => 604800, // 1 week in seconds
                         'path'     => '/',
-                        'domain'   => '', // Defaults to the current domain from $_SERVER
                     ),
                 ),
             ),
         ));
 
+The ``remember_me`` firewall defines the following configuration options:
+
+``key`` (default value: ``null``)
+    The value used to encrypt the cookie's content. It's common to use the
+    ``secret`` value defined in the ``app/config/parameters.yml`` file.
+
+``name`` (default value: ``REMEMBERME``)
+    The name of the cookie used to maintain the user logged in. If you enable the
+    "Remember Me" feature in several firewalls of the same application, make sure
+    to choose a different name for the cookie of each firewall. Otherwise, you'll
+    face lots of security related problems.
+
+``lifetime`` (default value: ``31536000``)
+    The number of seconds during which the user will remain logged in. By default
+    users are logged in for one year.
+
+``path`` (default value: ``/``)
+    The path where the cookie associated with this feature is used. By default
+    the cookie will be applied to the entire website but you can restrict to a
+    specific section (e.g. ``/forum``, ``/admin``).
+
+``domain`` (default value: ``null``)
+    The domain where the cookie associated with this feature is used. By default
+    cookies use the current domain obtained from ``$_SERVER``.
+
+``secure`` (default value: ``false``)
+    If ``true``, the cookie associated with this feature is sent to the user
+    through an HTTPS secure connection.
+
+``httponly`` (default value: ``true``)
+    If ``true``, the cookie associated with this feature is accessible only
+    through the HTTP protocol. This means that the cookie won't be accessible
+    by scripting languages, such as JavaScript.
+
+``remember_me_parameter`` (default value: ``_remember_me``)
+    The name of the form field checked to decide if the "Remember Me" feature
+    should be enabled or not. Keep reading this article to know how to enable
+    this feature conditionally.
+
+``always_remember_me`` (default value: ``false``)
+    If ``true``, the value of the ``remember_me_parameter`` is ignored and the
+    "Remember Me" feature is always enabled, regardless of the desire of the
+    end user.
+
+Forcing the User to Opt-Out of the Remember Me Feature
+------------------------------------------------------
+
 It's a good idea to provide the user with the option to use or not use the
 remember me functionality, as it will not always be appropriate. The usual
 way of doing this is to add a checkbox to the login form. By giving the checkbox