Disable symfony 2 csrf token protection on ajax submit

i'm building a mobile app talking to my symfony2 app via webservices I can't find a way to disable csrf protection on a specific controller/action

i want to post registration data to this action and use sf2 form validation. I do not call the form in my mobile app

Can't change container parameters in action, throw an exception because it is a frozen parameter...

I do not want to disable form protection for whole my application

any clue ?

thanks !

update: with symfony 2.1.x

/**
 * {@inheritdoc}
 */
public function setDefaultOptions(OptionsResolverInterface $resolver)
{
    $resolver->setDefaults(array(
        'csrf_protection'   => false,
    ));
}