$encoder = $this->container->get('security.password_encoder');
$encodedPwd = $encoder->encodePassword($adminUser, $plainPassword);

$adminUser = $this->getDoctrine()->getManager()->getRepository("AcmeUserBundle:AdminUser")->findOneBy(array('username' => $_username));
$_password = $request->request->get('_password');

$encoder = $this->container->get('security.password_encoder');
echo $encoder->isPasswordValid($adminUser, $_password))