node access

use Drupal\Core\Form\FormStateInterface;

function my_module_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  // Add default values for vapn module so the editor don't need to check this.
  if (isset($form['vapn']) && $form_state->getFormObject()->getEntity()->isNew()) {
    $form['vapn']['content']['widget']['#default_value'] = ['anonymous', 'authenticated'];
  }
}

use Drupal\node\Entity\Node;

function my_module_deploy_vapn_install() {
  $entity_type_manager = \Drupal::service('entity_type.manager');
  $role_storage = $entity_type_manager->getStorage('user_role');
  $node_storage = $entity_type_manager->getStorage('node');
  $nodes = $node_storage->loadByProperties([
    'type' => 'my_bundle'
  ]);

  $roles = array_values($role_storage->loadMultiple(['anonymous', 'authenticated']));
  foreach ($nodes as $node) {
    // First check if already some roles are set. Only needed if you are upgrading vapn.
    if ($node->vapn->isEmpty()) {
      $node->setSyncing(TRUE)
        ->set('vapn', $roles)
        ->save();
    }
  }
}