Action of webform displayed in modal opened by OpenModalDialogCommand in AjaxResponse

Question

I'm trying to open a webform in a modal by using OpenModalDialogCommand in an AjaxResponse like this.

• in buildForm method, I'm specifying AJAX callback like this:

$form['actions']['submit'] = [
  '#type' => 'submit',
  '#value' => $this->t('Send'),
  '#ajax' => [
    'callback' => [$form_state->getFormObject(), 'ajaxSubmitForm'],
    'disable-refocus' => TRUE,
    'progress' => 'none',
  ],
];

• in ajaxSubmitForm, I'm specifying AjaxResponse like this:

$output['webform'] = [
  '#type' => 'webform',
  '#webform' => 'contact',
  '#default_data' => [],
];
$response->addCommand(new OpenModalDialogCommand(
  'My title',
  $output,
  [
    'width' => '600px',
    'dialogClass' => 'social-dialog--task-webform',
  ]
));
return $response;

This works fine, but the action attribute of the <form> rendered in the modal is set to the path of the page, instead of the webform. Which results in HTML being returned in the AJAX response and the Drupal.AjaxError in the browser console. How can I fix this?

EDIT: I noticed, that views_ui core module defines a SetFormCommand, which allows for custom URL used when views form is displayed in the modal. Isn't something like this also needed for webform forms?

EDIT 2: So I tried to reimplement SetFormCommand for webform, but it's not working. Perhaps I'm limited by my insufficient knowledge of AJAX API in Drupal here.