现在小程序原生支持支付功能了，非常简单也不需要加密。

云函数

exports.main = async (event, context) => {
  const { totalFee } = event
  const res = await cloud.cloudPay.unifiedOrder({
    "body" : "学校-超市",
    "outTradeNo" : "1217752501201407033233368018",
    "spbillCreateIp" : "127.0.0.1",
    "subMchId" : "1900009231",
    "totalFee" : totalFee,
    "envId": "test-f0b102",
    "functionName": "pay_cb"
  })
  return res
}

小程序

Page({
    doPay: function(totalFee) {
        let that = this;
        ;(async () => {
            // 调用云函数
            let tradeRes = await wx.cloud.callFunction({
                name: 'pay',
                data: {
                    // ...
                    totalFee: totalFee,
                }
            })
            const payment = tradeRes.result.payment
            // 调用微信支付接口
            wx.requestPayment({
                ...tradeRes.result.payment,
                success (res) {
                    console.log('支付成功', res)
                },
                fail (res) {
                    console.error('pay fail', err)
                }
            })
        })();
    }
})