aa.php

<?
// ...

use Symfony\Component\Config\FileLocator;
use Symfony\Component\DependencyInjection\Loader\XmlFileLoader;

public function load(array $configs, ContainerBuilder $container)
{
    $loader = new XmlFileLoader($container, new FileLocator(dirname(__DIR__).'/Resources/config'));
    $loader->load('services.xml');

    $configuration = new Configuration();
    $config = $this->processConfiguration($configuration, $configs);

    $definition = $container->getDefinition('acme.social.twitter_client');
    $definition->replaceArgument(0, $config['twitter']['client_id']);
    $definition->replaceArgument(1, $config['twitter']['client_secret']);
}