Possibility to alter http headers when we generate PDF

I used this functionality successfull to add headers for my use case of wanting X-Robot-Tag added to every PDF generated by the module.

Here is an example

added to module services.yml:

my_custom.events:
    class: Drupal\my_custom\EventSubscriber\MyEventSubscriber
    tags:
      - { name: event_subscriber }

Then in the modules/custom/my_custom/src/EventSubscriber/MyEventSubscriber.php:

namespace Drupal\my_custom\EventSubscriber;

use Drupal\entity_print\Event\PrintEvents;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\EventDispatcher\GenericEvent;

/**
 * Add custom headers.
 */
class MyEventSubscriber implements EventSubscriberInterface {

  public static function getSubscribedEvents() {
    $events[PrintEvents::CONFIGURATION_ALTER][] = ['onEntityPrintConfigurationAlter'];
    return $events;
  }

  /**
   * React to an event fired when retrieving a Print engine configuration.
   *
   * @param \Symfony\Component\EventDispatcher\GenericEvent $event
   *   Generic event containing the print engine configuration.
   */
  public function onEntityPrintConfigurationAlter(GenericEvent $event) {
    $configuration = $event->getArgument('configuration');
    $configuration['headers']['X-Robot-Tag'] = 'noindex,nofollow,noarchive';
    $event->setArgument('configuration', $configuration);
  }
}

This was enough for me to have the headers appear on every PDF.

Changes from MR in combination with the event subscriber from #8 ✨ Possibility to alter http headers when we generate PDF Postponed: needs info work great for me.
Thanks!

I believe there is a typo in my code from #8 -- should be "X-Robots-Tag" and not "X-Robot-Tag"