public function generateCaptchaAction($key)
    {
        $options = $this->container->getParameter('gregwar_captcha.config');
        $session = $this->get('session');
        $whitelistKey = $options['whitelist_key'];
        $isOk = false;

        if ($session->has($whitelistKey)) {
            $keys = $session->get($whitelistKey);
            if (is_array($keys) && in_array($key, $keys)) {
                $isOk = true;
            }
        }

        if (!$isOk) {
            return $this->error($options);
        }

        /* @var \Gregwar\CaptchaBundle\Generator\CaptchaGenerator $generator */
        $generator = $this->container->get('gregwar_captcha.generator');

        $persistedOptions = $session->get($key, array());
        $options = array_merge($options, $persistedOptions);

        $phrase = $generator->getPhrase($options);
        $generator->setPhrase($phrase);
        $persistedOptions['phrase'] = $phrase;
        $session->set($key, $persistedOptions);

        $response = new Response($generator->generate($options));
        $response->headers->set('Content-type', 'image/jpeg');
        $response->headers->set('Pragma', 'no-cache');
        $response->headers->set('Cache-Control', 'no-cache');

        return $response;
    }