--- /dev/null
+<?php
+
+namespace Drupal\form_test\Form;
+
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Symfony\Component\HttpFoundation\JsonResponse;
+
+class FormTestInputForgeryForm extends FormBase {
+
+ /**
+ * {@inheritdoc}
+ */
+ public function getFormId() {
+ return '_form_test_input_forgery';
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function buildForm(array $form, FormStateInterface $form_state) {
+ // For testing that a user can't submit a value not matching one of the
+ // allowed options.
+ $form['checkboxes'] = [
+ '#title' => t('Checkboxes'),
+ '#type' => 'checkboxes',
+ '#options' => [
+ 'one' => 'One',
+ 'two' => 'Two',
+ ],
+ ];
+ $form['submit'] = [
+ '#type' => 'submit',
+ '#value' => t('Submit'),
+ ];
+
+ return $form;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function submitForm(array &$form, FormStateInterface $form_state) {
+ return new JsonResponse($form_state->getValues());
+ }
+
+}