protected function configureFormFields(FormMapper $formMapper)
{
    $formMapper
        ......
        ->add('plainPassword', 'repeated', array(
            'type' => 'password',
            'options' => array('translation_domain' => 'FOSUserBundle'),
            'first_options' => array('label' => 'form.password'),
            'second_options' => array('label' => 'form.password_confirmation'),
            'invalid_message' => 'fos_user.password.mismatch',
                'required'    => false,
            )
        )
        ..
}