function is_https() {

    if ( !empty($_SERVER['HTTPS']) && strtolower($_SERVER['HTTPS']) !== 'off') {

        return true;

    } elseif ( isset($_SERVER['HTTP_X_FORWARDED_PROTO']) && $_SERVER['HTTP_X_FORWARDED_PROTO'] === 'https' ) {

        return true;

    } elseif ( !empty($_SERVER['HTTP_FRONT_END_HTTPS']) && strtolower($_SERVER['HTTP_FRONT_END_HTTPS']) !== 'off') {

        return true;

    }

    return false;

}