PHP后台调用微信支付下单
function wx_getPayRequest($openid, $orderid, $rmb, $title,$appoids)
{
    $nonce   = $orderid.mt_rand(10000,99999);
    $orderid=$orderid.'_'.$nonce;//str_replace(",","_",$appoids);
    //Log::write('\n ================'.$orderid,'notice');
    $srct='0x'.md5(config('app.environment')['paykey'].$orderid);
    $notify  = '';//回调地址，自己写，支付成功回调，在回调页面进行更改与用户金钱相关的代码
    $url= 'https://api.mch.weixin.qq.com/pay/unifiedorder';//统一接口prepay_id
    // post data
    $now  = time().'';//时间
    $appid ='';//小程序ID 写到一个类里面了 方便后期修改 当然也可以在这里直接写
    $mchid ='';//商户号
   // Log::write('\n $mchid================'.json_encode($mchid),'notice');
   // Log::write('\n $appid================'.json_encode($appid),'notice');
    $data = array(
        'appid'            => $appid,
        'mch_id'           => $mchid,
        'spbill_create_ip' => '127.0.0.1',//终端ip   Y
        'nonce_str'        => $nonce,                //随机字符串Y
        'openid'           => $openid,               //用户标识 N
        'body'             => $title,                //商品描述 Y
        // 'detail'           => $body,                 //商品详情 N
        'attach'           => $appoids,              //附加数据 N
        'out_trade_no'     => $orderid,              //商户订单号 Y
        'total_fee'        => $rmb,                  //总金额 单位分 int Y
        'notify_url'       => $notify,               //通知地址 Y
        'trade_type'       => 'JSAPI',
    );

    $data[ 'sign' ] = self::MakeSign($data);
    //echo $data[ 'sign' ];
   // Log::write('\n sign================'.json_encode($data[ 'sign' ]),'notice');

    $xml=self::wx_toXML($data);
    $ret = $this->http_request($url,$xml);
    $json = self::wx_parseXML( $ret );
    //Log::write('\n ================'.json_encode($json),'notice');
    if( !$json || !isset($json[ 'prepay_id' ]) )
    {
        return array( 'payCode'=>1,'ret' => 'fail', 'tip' => $json[ 'return_msg' ] );
    }

    $prepayid = $json[ 'prepay_id' ];
    $req = array(
        'appId'     => $appid,
        'timeStamp' => $now,
        'nonceStr'  => $nonce,
        'package'   => 'prepay_id='.$prepayid,
        'signType'  => 'MD5',
    );
    $req[ 'paySign' ] = self::wx_getPkgSign($req);
    //$req[ 'notify' ] = $notify;
    return $req;
}

///作用：格式化参数，签名过程需要使用
private function formatBizQueryParaMap($paraMap, $urlencode) {
    $buff = "";
    ksort($paraMap);
    foreach ($paraMap as $k => $v) {
        if ($urlencode) {
            $v = urlencode($v);
        }
        $buff .= $k . "=" . $v . "&";
    }
    $reqPar;
    if (strlen($buff) > 0) {
        $reqPar = substr($buff, 0, strlen($buff) - 1);
    }
    return $reqPar;
}


public function wx_getPkgSign($req )
{
    foreach ($req as $k => $v) {
        $Parameters[$k] = $v;
    }
    //签名步骤一：按字典序排序参数
    ksort($Parameters);
    $String = $this->formatBizQueryParaMap($Parameters, false);
    //签名步骤二：在string后加入KEY
    $String = $String . "&key=" . config('app.environment')['paykey'];
    //签名步骤三：MD5加密
    $String = md5($String);
    //签名步骤四：所有字符转为大写
    $result_ = strtoupper($String);
    return $result_;
}

public  function wx_toXML( $data )
{
    $xml = '<xml>';
    foreach( $data as $key => $val )
    {
        $xml .= '<' . $key . '><![CDATA[' . $val . ']]></' . $key . '>';
    }
    $xml .= '</xml>';
    return $xml;
}

/**
 * 输出xml字符
 * @param $data
 * @return string
 */
public function ToXml($data)
{
    if(!is_array($data)
        || count($data) <= 0)
    {
        throw new WxPayException("数组数据异常！");
    }

    $xml = "<xml>";
    foreach ($data as $key=>$val)
    {
        if (is_numeric($val)){
            $xml.="<".$key.">".$val."</".$key.">";
        }else{
            $xml.="<".$key."><![CDATA[".$val."]]></".$key.">";
        }
    }
    $xml.="</xml>";
    return $xml;
}

/**
 * 格