Grav\Plugin\Admin\AdminController::taskLogin PHP Method

    protected function taskLogin()
    {
        $this->data['username'] = strip_tags(strtolower($this->data['username']));
        if ($this->admin->authenticate($this->data, $this->post)) {
            // should never reach here, redirects first
        } else {
            $this->admin->setMessage($this->admin->translate('PLUGIN_ADMIN.LOGIN_FAILED'), 'error');
        }
        return true;
    }