Create access plugin

spaint_iframe.module

/**
 * Implements hook_ctools_plugin_directory().
 */
function spaint_iframe_ctools_plugin_directory($module, $plugin) {
  if ($module == 'ctools' || $module == 'panels' || $module == 'page_manager') {
    return 'plugins/' . $plugin;
  }
  // Safety: go away if CTools is not at an appropriate version.
  if (!module_invoke('ctools', 'api_version', VUD_REQUIRED_CTOOLS_API)) {
    return;
  }
  if (in_array($module, array('ctools', 'panels', 'entityreference'))) {
    return "plugins/$module/$plugin";
  }
}

/**
 * Implements hook_ctools_plugin_api().
 */
function spaint_iframe_ctools_plugin_api($owner, $api) {
  if ($owner == 'panels') {
    return array('version' => 2.0);
  }
  if ($owner == 'metatag' && $api == 'metatag') {
    return array('version' => 1);
  }
}

/**
 * In plugin directory.
 */
$plugin = array(
  'title' => t('iframe vk app'),
  'description' => t('Is page opened in iframe'),
  'callback' => 'spaint_iframe_app_callback',
  'summary' => 'spaint_iframe_app_access_summary',
);

/**
 * Callback.
 */
function spaint_iframe_app_callback($conf, $context) {
  return spaint_site_is_app();
}

/**
 * Describe an instance of this plugin.
 */
function spaint_iframe_app_access_summary($conf, $context) {
  return t('Grant access only if user is customer or seller.');
}