wallabag/src/Wallabag/UserBundle/DependencyInjection/Configuration.php

<?php

namespace Wallabag\UserBundle\DependencyInjection;

use Symfony\Component\Config\Definition\Builder\TreeBuilder;
use Symfony\Component\Config\Definition\ConfigurationInterface;

class Configuration implements ConfigurationInterface
{
    public function getConfigTreeBuilder()
    {
        $treeBuilder = new TreeBuilder();
        $rootNode = $treeBuilder->root('wallabag_user');

        $rootNode
            ->children()
                ->booleanNode('registration_enabled')
                    ->defaultValue(true)
                ->end()
            ->end()
        ;

        return $treeBuilder;
    }
}