How to use Namespaced Sessions in Symfony2

Since Symfony 3, the override of session.attribute_bag.class parameter doesn't work anymore.

The solution I applied after pulling my hair for a few time is using a compiler pass to override the session.attribute_bag service class.

I did it in the Kernel directly, but an external compiler pass would work the same way.

SF4 Kernel

<?php
// src/Kernel.php
namespace App;

use Symfony\Bundle\FrameworkBundle\Kernel\MicroKernelTrait;
use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\HttpKernel\Kernel as BaseKernel;
use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
use Symfony\Component\HttpFoundation\Session\Attribute\NamespacedAttributeBag;

class Kernel extends BaseKernel implements CompilerPassInterface
{
    use MicroKernelTrait;

    // ...

    public function process(ContainerBuilder $container)
    {
        $container->getDefinition('session.attribute_bag')->setClass(NamespacedAttributeBag::class);
    }
}

Just open your config.yml and after imports add:

parameters:
    session.attribute_bag.class: Symfony\Component\HttpFoundation\Session\Attribute\NamespacedAttributeBag

It looks like this:

imports:
    - { resource: parameters.yml }
    - { resource: security.yml }

parameters:
    session.attribute_bag.class: Symfony\Component\HttpFoundation\Session\Attribute\NamespacedAttributeBag

framework:
# ...

Because it's also possible to use the HTTPFoundation Component outside of Symfony2, the way to implement NamespacedUserBags is as follows:

use Symfony\Component\HttpFoundation\Session\Session;
use Symfony\Component\HttpFoundation\Session\Attribute\NamespacedAttributeBag;

$session = new Session();

//first bag
$myAttributeBag = new NamespacedAttributeBag('<your_storage_key_1>');
$myAttributeBag->setName('<your_tag_name_1>');
$session->registerBag($myAttributeBag);

//second bag
$myAttributeBag = new NamespacedAttributeBag('<your_storage_key_2>');
$myAttributeBag->setName('<your_tag_name_2>');
$session->registerBag($myAttributeBag);

$session->start();

Register as many bags as you want, but make sure to do this before you start the session. Now you can switch between bags using getBag():

$activeBag = $session->getBag('<your_tag_name>');

and access the namespaced bag with the typical methods :

$activeBag->set('tokens/a', 'adsf82983asd');
$activeBag->set('tokens/b', 'daslfl232l3k');

print_r($activeBag->get('tokens'));

You should redefine session service and also define service for your attribute bag (if you'll check default implementation of session.attribute_bag you'll see that this service has only class attribute).

And inject your new service to redefined session service into there

services:
    session:
        class: Symfony\Component\HttpFoundation\Session\Session
        arguments:
            - @session.storage
            - @your.session.attribute_bag #service id is defined below
            - @session.flash_bag

    your.session.attribute_bag:
        class: Symfony\Component\HttpFoundation\Session\Attribute\NamespacedAttributeBag