Event does not trigger each time I load a page

Question

I'm using event dispatcher in a custom module to auto login users in a Drupal 8 website. I'm using the KernelEvents::REQUEST, with a onRequest fonction. I put an echo for testing that the function was call :

• When the user is already log in, the event work and my function was call on every request
• When the user IS NOT log in (anonymous), the function was call on the only first request of a page. Never call again if you reload the page. Only way to get my echo again is to empty drupal cache (I make a drush cr).

Don't know exactly how Drupal cache work... Is there any way to trigger my event on every request, anonymous or not ? Or another better way to do my auto login ? Thanks.

my module structure :

/mymodule
|-- /src
|---- /Controller
|------ MyModuleController.php
|---- /EventSubscriber
|------ MyModuleEventSubscriber.php
mymodule.info.yml
mymodule.routing.yml
mymodule.services.yml

MyModuleEventSubscriber.php

<?php

namespace Drupal\mymodule\EventSubscriber;

use Drupal\Core\Routing\ResettableStackedRouteMatchInterface;
use Drupal\Core\Session\AccountProxyInterface;
use Drupal\externalauth\ExternalAuthInterface;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\GetResponseEvent;
use Symfony\Component\HttpKernel\KernelEvents;
use Symfony\Component\HttpFoundation\RedirectResponse;

class MyModuleEventSubscriber implements EventSubscriberInterface {

  protected $currentRouteMatch;
  protected $externalauth;
  protected $currentUser;

  /**
   * Constructs a MyModuleEventSubscriber object.
   */
  public function __construct(ResettableStackedRouteMatchInterface $currentRouteMatch, ExternalAuthInterface $externalauth, AccountProxyInterface $currentUser) {
    $this->currentRouteMatch = $currentRouteMatch;
    $this->externalauth = $externalauth;
    $this->currentUser = $currentUser;
  }

  /**
   * Implements EventSubscriberInterface::getSubscribedEvents().
   *
   * @return array
   *   An array of event listener definitions.
   */
  static function getSubscribedEvents() {
    $events[KernelEvents::REQUEST][] = array('onRequest');
    return $events;
  }

  public function onRequest(GetResponseEvent $event) {
      // echo 'test' => do my echo here
      if ($this->currentUser->id() == '0') {       
         auto_login(); // I simplified the code here, but you get the idea
      }      
  }
}

mymodule.services.yml

services:
  mymodule.event_subscriber:
    class: Drupal\mymodule\EventSubscriber\MyModuleEventSubscriber
    arguments: ['@current_route_match', '@externalauth.externalauth', '@current_user']
    tags:
      - { name: event_subscriber }

Answer 1

This look like it is the module "Internal Page Cache", which caches pages for anonymous users. This cache runs before any event as middleware.

In your case there is no need for this module and you can uninstall it.

If there is other code that does interfere you should be able to control this with a priority you set on the event subscriber.