class ExampleConfigEntityExternalForm

class ExampleConfigEntityExternalForm extends FormBase {
  
  /**
   * Tempstore factory.
   *
   * @var \Drupal\Core\TempStore\SharedTempStoreFactory
   */
  protected $tempstore;
  
  /**
   * Constructs a new ExampleConfigEntityExternalForm.
   *
   * @param \Drupal\ctools_wizard_test\Form\SharedTempStoreFactory $tempstore
   *   Creates a shared temporary storage for a collection.
   */
  public function __construct(SharedTempStoreFactory $tempstore) {
    $this->tempstore = $tempstore;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static($container->get('tempstore.shared'));
  }
  
  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'ctools_wizard_test_example_config_entity_external_form';
  }
  
  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state, $machine_name = '') {
    $cached_values = $this->tempstore
      ->get('ctools_wizard_test.config_entity')
      ->get($machine_name);
    /** @var \Drupal\ctools_wizard_test\Entity\ExampleConfigEntity $page */
    $config_entity = $cached_values['ctools_wizard_test_config_entity'];
    $form['blah'] = [
      '#markup' => 'Value from one: ' . $config_entity->getOne(),
    ];
    return $form;
  }
  
  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    // Don't do anything.
  }

}