1. 接口： http://xxx.xxx.cn/index.php/Common/apiAlipay；

APP端只需传入排好的订单的串：

public function apiAlipay(){
        $home_path = realpath(dirname(__FILE__).'/../');   // /data/wwwroot/jinling/home
        //require_once ($home_path.'/alipay-sdk-PHP-20180104135052/AopSdk.php');
        //require $home_path.'/alipay-sdk-PHP-20180104135052/aop/AopClient.php';
        require $home_path .'/libraries/alipay/AopClient.php';
        $data['orderInfo'] = $this->input->post('orderInfo');   // 订单信息，在iOS端加密
        $c = new AopClient;
        $c->gatewayUrl = "https://openapi.alipay.com/gateway.do";
        $c->appId = "";   // 填写你的AppID
        $c->rsaPrivateKey = '';  // 应用私钥  在生成私钥的时候看清是java还是非java端
        $c->format = "json";
        $c->charset = "UTF-8";
        $c->signType= "RSA2";   // 这里看清到底是用RSA 还是 RSA2
        $c->alipayrsaPublicKey = '';  // 是支付宝公钥！不是应用公钥！
        exit(json_encode(array('data'=>$c->rsaSign($data['order_no'],'RSA2')),true));
}

还存在的问题：使用最新的sdk不行，得用相对应的SDK

2. iOS端传入的orderInfo 如下 ：

app_id=20180106xxxx7555&
biz_content={ "seller_id": "", "total_amount": "0.01", "subject": "标题", "out_trade_no": "MD2018020413415411744", "timeout_express": "30m", "product_code": "QUICK_MSECURITY_PAY" }&
charset=utf-8&
method=alipay.trade.app.pay&
notify_url=http://jinling.veyd.cn/index.php/AliPay/notify&
sign_type=RSA2&
timestamp=2018-02-04 13:41:54&
version=1.0

image.png