The 'Web Authentification' button is not working on the login form component (example: https://t4-framework.demo.joomlart.com/index.php/joomla-pages/bonus-pages/login-page). Adding id="com-users-loginform" will make it works (default_login.php):
<form action="<?php echo Route::_('index.php?option=com_users&task=user.login'); ?>" method="post" class="frm-login-form form-validate" id="com-users-login__form">