Loading a form using Ctools AJAX API

custom.module.php

function custom_menu() {
  $items['custom_module/some_title_describing_action/%ctools_js'] = array(
      'title' => 'Subscribe',
      'page callback' => 'custom_form__callback',
      'page arguments' => array(2), // index starts with zero
      'type' => MENU_CALLBACK,
      'access callback' => TRUE
    );
    
    return $items;
}

function custom_form__callback($js = FALSE) {
    ctools_include('modal'); // Mandatory
    ctools_include('ajax'); // Mandatory
    if (!js) {
        return drupal_get_form('FORM_ID', $form_state);
    }
    $form_state = array(
        'title' => t('TITLE'),
        'ajax' => TRUE
        );
    $output = ctools_modal_form_wrapper('ID_OF_WEBFORM-FUNCTION_RETURNING_A_WEBFORM', $form_state);
    if (!empty($form_state['executed'])) { // If form is submitted
        $output = array();
        $output[] = ajax_command_html('JQUERY_SELECTOR', t('SOME_TITLE'));
        /*Here goes, basically, any Drupal.AJAX commands that operates the content on a page*/
    }
    print ajax_render($output);
    exit();
}

// Hook into submitting form process
function FORM_ID_submit(&$form, &$form_state) {
    if ($form_state['ajax'] == TRUE) {
        // We are using AJAX powered form
        drupal_set_message(t('LOOKS COOL, DUDE!'), 'status', FALSE);
    } else {
      /* We got a bareboned form without JS. Basically, JS is turned off or
       form opened as a standalone node */
        drupal_goto('/');
      // Do whateva
       
    }
    
}