hasSession($request); $page_top['session_exists_cache_context_test'] = [ 'label' => [ '#markup' => '

' . ($session_exists ? 'Session exists!' : 'Session does not exist!') . '

', ], 'cache_context_value' => [ '#markup' => '[session.exists]=' . \Drupal::service('cache_context.session.exists')->getContext() . '', ], ]; if (\Drupal::request()->query->get('trigger_session')) { $_SESSION['session_exists_cache_context_test'] = TRUE; } }