微信支付退款 PHP

退款需要双向证书，再商户平台-》API安全-》下载证书

$config = array(
            'mch_id' => "商户ID",
            'appid' => "appid",
            'key' => "APIKEY",
        );
        $unified = array(
            'appid' => "APPID", 
            'mch_id' => "商户ID",
            'nonce_str' => md5(time()),
            'total_fee' => 1,       //订单金额    单位 转为分
            'refund_fee' => 1,       //退款金额 单位 转为分
            'sign_type' => 'MD5',           //签名类型 支持HMAC-SHA256和MD5，默认为MD5
            'out_trade_no'=> $order_id,        //商户订单号
            'out_refund_no'=>'re_'.time(),        //商户退款单号
            'refund_desc'=>'退款原因',     //退款原因（选填）,
            'notify_url' => 'github.com' //退款成功回调地址
        );
        $unified['sign'] = $this->getSign($unified, $config['key']);
        $responseXml = $this->curlPost('https://api.mch.weixin.qq.com/secapi/pay/refund', $this->arrayToXml($unified));
        $unifiedOrder = simplexml_load_string($responseXml, 'SimpleXMLElement', LIBXML_NOCDATA);

        if ($unifiedOrder === false) {
            die('parse xml error');
        }
        if ($unifiedOrder->return_code != 'SUCCESS') {
            die($unifiedOrder->return_msg);
        }
        if ($unifiedOrder->result_code != 'SUCCESS') {
            die($unifiedOrder->err_code);
        }

在这里设置

function curlPost($url = '', $postData = '', $options = array())
    {
        if (is_array($postData)) {
            $postData = http_build_query($postData);
        }
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
        curl_setopt($ch, CURLOPT_POST, 1);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $postData);
        curl_setopt($ch, CURLOPT_TIMEOUT, 30); //设置cURL允许执行的最长秒数
        if (!empty($options)) {
            curl_setopt_array($ch, $options);
        }
        //https请求 不验证证书和host
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
        curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
        //第一种方法，cert 与 key 分别属于两个.pem文件
        //默认格式为PEM，可以注释
        curl_setopt($ch,CURLOPT_SSLCERTTYPE,'PEM');
        curl_setopt($ch,CURLOPT_SSLCERT,getcwd().'/cert/apiclient_cert.pem');//证书路径
        //默认格式为PEM，可以注释
        curl_setopt($ch,CURLOPT_SSLKEYTYPE,'PEM');
        curl_setopt($ch,CURLOPT_SSLKEY,getcwd().'/cert/apiclient_key.pem');//证书路径
        //第二种方式，两个文件合成一个.pem文件
//        curl_setopt($ch,CURLOPT_SSLCERT,getcwd().'/all.pem');
        $data = curl_exec($ch);
        curl_close($ch);
        return $data;
    }