微信小程序获取openid

https://api.weixin.qq.com/sns/jscode2session?appid=APPID&secret=SECRET&js_code=JSCODE&grant_type=authorization_code

wx.login({
  success: res => {
    console.log(res);   //用户登录凭证 
    // 发送 res.code 到后台换取 openId, sessionKey
    var code = res.code;
    var appid = 'xxxxx';    //小程序的appid
    var secret = 'xxxxx';   //小程序的secret
    wx.request({
      url: 'https://api.weixin.qq.com/sns/jscode2session?appid='+appid+'&secret='+secret+'&grant_type=authorization_code&js_code='+code,
      header: { 'content-type': 'application/json' },
      success:function(res){
        console.log(res);   // 返回的数据
        console.log(res.data.openid);   // openid
      }
    })
  }
})

需要把这个接口，写到后台去

        wx.login({
            success: function (res) {
              console.log(res)
              wx.request({
                url: '后台通过获取前端传的code返回openid的接口地址',
                data: { code: code },
                method: 'POST',
                header: { 'content-type': 'application/json'},
                success: function (res) {
                 if (res.statusCode == 200) {
                   console.log(res.data.result.openid);
                   console.log(res.data.result.unionid);
                 } else {
                   console.log(res.errMsg)
                 }
              },
            })
          }
       })