//签名
    function sin($params){
        ksort($params);
        $str = '';
        foreach ($params as $key => $param) {
            if ($param === '') continue;
            $param=urlencode($param);
            $str .= (empty($str) ? '' : '&') . "{$key}={$param}";
        }
        // $str.='channelcode='.$params['channelcode'].'&productcode='.$params['productcode'].'&orderno='.$params['orderno'].'&appsecret=Mi1TtL0YyQbqom3xQjOrT2RD7KCPHmel';
        $str.='&Mi1TtL0YyQbqom3xQjOrT2RD7KCPHmel';
        $md5 = md5($str);
        return $md5;
    }