Method getLoginButtons

/**
 * Get additional login buttons to add in a login module. These buttons can be used for
 * authentication methods external to Joomla such as WebAuthn, login with social media
 * providers, login with third party providers or even login with third party Single Sign On
 * (SSO) services.
 *
 * Button definitions are returned by the onUserLoginButtons event handlers in plugins. By
 * default, only system and user plugins are taken into account. The former because they are
 * always loaded. The latter are explicitly loaded in this method.
 *
 * The onUserLoginButtons event handlers must conform to the following method definition:
 *
 * public function onUserLoginButtons(string $formId): array
 *
 * The onUserLoginButtons event handlers must return a simple array containing 0 or more button
 * definitions.
 *
 * Each button definition is a hash array with the following keys:
 *
 * * `label`   The translation string used as the label and title of the button. Required
 * * `id`      The HTML ID of the button. Required.
 * * `tooltip` (optional) The translation string used as the alt tag of the button's image
 * * `onclick` (optional) The onclick attribute, used to fire a JavaScript event. Not
 *             recommended.
 * * `data-*`  (optional) Data attributes to pass verbatim. Use these and JavaScript to handle
 *             the button.
 * * `icon`    (optional) A CSS class for an optional icon displayed before the label; has
 *             precedence over 'image'
 * * `image`   (optional) An image path for an optional icon displayed before the label
 * * `class`   (optional) CSS class(es) to be added to the button
 *
 * You can find a real world implementation of the onUserLoginButtons plugin event in the
 * system/webauthn plugin.
 *
 * You can find a real world implementation of consuming the output of this method in the
 * modules/mod_login module.
 *
 * Third party developers implementing a login module or a login form in their component are
 * strongly advised to call this method and consume its results to display additional login
 * buttons. Not doing that means that you are not fully compatible with Joomla 4.
 *
 * @param   string  $formId  The HTML ID of the login form container. Use it to filter when and
 *                           where to show your additional login button(s)
 *
 * @return  array  Button definitions.
 *
 * @since   4.0.0
 */
public static function getLoginButtons(string $formId) : array
{
    // Get all the User plugins.
    PluginHelper::importPlugin('user');
    // Trigger the onUserLoginButtons event and return the button definitions.
    try {
        /** @var CMSApplication $app */
        $app = Factory::getApplication();
    } catch (Exception $e) {
        return [];
    }
    $results = $app->triggerEvent('onUserLoginButtons', [$formId]);
    $buttons = [];
    foreach ($results as $result) {
        // Did we get garbage back from the plugin?
        if (!is_array($result) || empty($result)) {
            continue;
        }
        // Did the developer accidentally return a single button definition instead of an array?
        if (array_key_exists('label', $result)) {
            $result = [$result];
        }
        // Process each button, making sure it conforms to the required definition
        foreach ($result as $item) {
            // Force mandatory fields
            $defaultButtonDefinition = ['label' => '', 'tooltip' => '', 'icon' => '', 'image' => '', 'class' => '', 'id' => '', 'onclick' => ''];
            $button = array_merge($defaultButtonDefinition, $item);
            // Unset anything that doesn't conform to a button definition
            foreach (array_keys($button) as $key) {
                if (substr($key, 0, 5) == 'data-') {
                    continue;
                }
                if (!in_array($key, ['label', 'tooltip', 'icon', 'image', 'svg', 'class', 'id', 'onclick'])) {
                    unset($button[$key]);
                }
            }
            // We need a label and an ID as the bare minimum
            if (empty($button['label']) || empty($button['id'])) {
                continue;
            }
            $buttons[] = $button;
        }
    }
    return $buttons;
}