private static function _getUserExtraFields(){
        if (!self::$extraFields){
            $proctoringExtension = \common_ext_ExtensionsManager::singleton()->getExtensionById('taoProctoring');
            $userExtraFields = $proctoringExtension->getConfig('monitoringUserExtraFields');
            $userExtraFieldsSettings = $proctoringExtension->getConfig('monitoringUserExtraFieldsSettings');
            if(!empty($userExtraFields) && is_array($userExtraFields)){
                foreach($userExtraFields as $name => $uri){
                    $property = new \core_kernel_classes_Property($uri);
                    $settings = array_key_exists($name, $userExtraFieldsSettings) ?
                        $userExtraFieldsSettings[$name] : [];
                    self::$extraFields[] = array_merge(array(
                        'id' => $name,
                        'property' => $property,
                        'label' => $property->getLabel(),
                    ), $settings);
                }
            }
        }

        return self::$extraFields;
    }