PHP实现微信小程序支付完整版，可以借鉴！

var url = getApp().globalData.httpServer + 'api/buy/pay';
   var userId = getApp().globalData.userId;
   var totalMoney = this.data.totalMoney;
   var cart = this.data.goods;
   var param = {
     cart: JSON.stringify(cart),
     cartamount: totalMoney,
     userid: userId,
     payment: this.data.payment,
     addressid: defaultAddress.id
   };
   var that = this;
   util.http(url, param, function (ret) {
     if (ret.data.code == 1) {
       if (that.data.payment == 'balance') { // 余额支付
         that.afterPaySuccess(ret.data.data);
       } else {                // 微信支付
         wx.requestPayment({
           timeStamp: ret.data.data.timeStamp,
           nonceStr: ret.data.data.nonceStr,
           package: ret.data.data.package,
           signType: ret.data.data.signType,
           paySign: ret.data.data.paySign,
           'success': function (res) {
             that.afterPaySuccess(ret.data.data.orderid);
           },
           'fail': function (res) {
             console.log(res);
           }
         })          


       }

     } else {
       util.showTip(ret.data.msg, '提交订单失败');        
     }
   });

/**
 * 网络请求
 */
function http(url, params, callback) {
  wx.request({
    url: url,
    data: params,
    success: function (res) {
      callback(res);
    },

    fail: function (err) {
      console.log(err);
    }
  });
}

public function pay()
{
  $cart = I('cart', '', 'trim');
  $cartAmount = I('cartamount');
  $addressId = I('addressid', 0, 'intval');
  $payment = I('payment', '', 'trim');
  $userId = $this->userid;

  $cart = json_decode($cart, true);
  if (empty($cart)) {
    $result['msg'] = '购物车获取失败';
    $result['code'] = 0;
    $this->ajaxReturn($result);
  }

  $totalMoney = 0;
  foreach ($cart as $goods) {
    $money = $goods['price'];  // price
    $selectCount = $goods['selectcount'];  // price
    $itemAmount = number_format($money * $selectCount, 2, '.', '');
    $totalMoney += $itemAmount;
  }
  // 检查总金额是否一致
  if ($totalMoney != $cartAmount) {
    $result['msg'] = '总金额不匹配:' . $totalMoney;
    $result['code'] = 0;
    $this->ajaxReturn($result);
  }

  // 获取用户地址
  $address = M('MemberAddress')->where('userid=' . $userId . " and id=" . $addressId)->find();
  if (empty($address)) {
    $result['msg'] = '用户地址不存在';
    $result['code'] = 0;
    $this->ajaxReturn($result);
  }

  // 用户信息
  $user = M('Member')->where("id=" . $userId)->find();
  if ($payment == 'balance') {
    if ($user['amount'] < $cartAmount) {
      $result['msg'] = '余额不足';
      $result['code'] = 0;
      $this->ajaxReturn($result);
    }
  }

  // 生成订单
  $order['ordersn'] = $this->genOrdersn($user['id']);
  $order['price'] = $cartAmount;
  $order['addressid'] = $address['id'];
  $order['addressinfo'] = serialize($address); //json_encode($address);
  $order['longitude'] = $address['longitude'];
  $order['latitude'] = $address['latitude'];
  $order['addtime'] = time();
  $order['status'] = 0;
  $order['userid'] = $user['id'];
  $order['paytype'] = $payment;
  $order['paysn'] = '';
  $order['paytime'] = time();
  $orderId = M("Order")->add($order);
  if ($orderId == 0) {
    $result['msg'] = '创建订单失败';
    $result['code'] = 0;
    $this->ajaxReturn($result);
  }
  foreach ($cart as $goods) {
    $orderGoods['orderid'] = $orderId;
    $orderGoods['goodsid'] = $goods['id'];
    $orderGoods['title'] = $goods['title'];
    $orderGoods['price'] = $goods['price'];
    $orderGoods['attr'] = $goods['attr'];
    $orderGoods['pic'] = $goods['pic'];
    $orderGoods['num'] = $goods['selectcount'];
    M("OrderGoods")->add($orderGoods);
  }

  if ($payment == 'balance') {
    // 余额支付
    $this->balancePay($cartAmount, $user['wxopenid'], $orderId);
  } else if ($payment == 'weixin') {
    // 微信支付
    $this->weixinPay($cartAmount, $user['wxopenid'], $orderId, $order['ordersn']);
  }
}

/**
   * 微信支付
   * @author 大脸猫脸大
   * @param $cart
   * @param $cartAmount
   * @param $address
   * @param $user
   */
  private function weixinPay($cartAmount, $openId, $orderId, $orderSn)
  {

    import("Vendor.Wxpay.lib.WxPay#Api", "", ".php");
    //订单号
    $money = $cartAmount * 100;
    $openid = $openId;
    $input = new \WxPayUnifiedOrder();
    $input->SetBody("迪克-商品");
    $input->SetOut_trade_no("$orderSn");
    $input->SetTotal_fee("$money");
    $input->SetNotify_url("https://" . $_SERVER['HTTP_HOST'] . "/api/buy/payNotify");
    $input->SetTrade_type("JSAPI");
    $input->SetOpenid($openid);
    $unifiedOrder = \WxPayApi::unifiedOrder($input);

    if ($unifiedOrder['result_code'] == 'SUCCESS' && $unifiedOrder['return_code'] == 'SUCCESS') {
      $time = time();
      $data['timeStamp'] = "$time";              //时间戳
      $data['nonceStr'] = $unifiedOrder['nonce_str'];     //随机字符串
      $data['signType'] = 'MD5';                //签名算法，暂支持 MD5
      $data['package'] = 'prepay_id=' . $unifiedOrder['prepay_id'];  //统一下单接口返回的 prepay_id 参数值，提交格式如：prepay_id=*
      $data['paySign'] = $this->genPaySign($unifiedOrder, $time);// 之前以为是$unifiedOrder['sign']; 后来发现是调用的这种方法. 签名方案参见微信公众号支付帮助文档;

      $data['out_trade_no'] = $orderSn; 
      $data['orderid'] = $orderId; 
      $return['code'] = 1; 
      $return['data'] = $data; 
    } else { 
        Log::write(var_export($unifiedOrder, true), Log::ERR, '', C('LOG_PATH')."wx_pay_".date('y_m_d').'.log'); 
        $return['code'] = 0; 
        $return['msg'] = '微信支付失败';// $unifiedOrder['RETURN_MSG']; 
    } 
    $this->ajaxReturn($return); 
}

/* 生成支付签名*/
private function genPaySign($unifiedOrder, $time)
{
  $appId = \WxPayConfig::APPID;
  $nonceStr = $unifiedOrder['nonce_str'];
  $package = 'prepay_id=' . $unifiedOrder['prepay_id'];
  $signType = "MD5";
  $timeStamp = $time;
  $key = \WxPayConfig::KEY;

  $sign = md5(sprintf("appId=%s&nonceStr=%s&package=%s&signType=%s&timeStamp=%s&key=%s", $appId, $nonceStr, $package, $signType, $timeStamp, $key));
}

/**
   * 支付回调
   * @author:大脸猫脸大
   */
  public function payNotify()
  {
    import("Vendor.Wxpay.lib.WxPay#Data", "", ".php");
    $xml = $GLOBALS['HTTP_RAW_POST_DATA'];
    $val = \WxPayResults::Init($xml);

    if ($val['result_code'] == 'SUCCESS' && $val['return_code'] == 'SUCCESS') {

      $orderSn = $val['out_trade_no'];
      $transactionId = $val['transaction_id'];
      $data = array('paytype' => 'weixin', 'status' => '1', 'paytime' => time(), 'paysn' => $transactionId);

      M("Order")->where("ordersn='$orderSn'")->setField($data);
      exit('<xml><return_code><![CDATA[SUCCESS]]></return_code><return_msg><![CDATA[OK]]></return_msg></xml>');
    }else {
      Log::write(var_export($val, true), Log::ERR, '', C('LOG_PATH')."wx_pay_notify_".date('y_m_d').'.log');
      exit('<xml><return_code><![CDATA[FAIL]]></return_code><return_msg><![CDATA[OK]]></return_msg></xml>');
    }
}

<xml><return_code><![CDATA[SUCCESS]]></return_code><return_msg><![CDATA[OK]]></return_msg></xml>