sessionless-1.x-dev/modules/sessionless_forms/sessionless_forms.module

<?php

use Drupal\Core\Form\FormStateInterface;
use Drupal\sessionless_forms\SessionlessFormHiddenFieldHandler;

/**
 * Implements hook_form_alter().
 *
 * Sorry, kittens: In form cache, we have no access to form array.
 * So add encrypted form fields that are linked to form state items.
 */
function sessionless_forms_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  SessionlessFormHiddenFieldHandler::hookFormAlter($form, $form_state, $form_id);
}