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.
    }

}