wx.login({
      success: function (res) {
        if (res.code) {
          // console.log(url.baseURL)
          // console.log(res.code)
          wx.request({
            url: '请求地址',
            method: 'POST',
//传给后端的参数，来换取用户信息
            data: {
              code: res.code,
              ip: ip,
              city: city,
              authorization: token
            },
            header: {
              'content-type': 'application/x-www-form-urlencoded' // 默认值
            },
            success: function (res) {
//res内打印用户信息，要传什么问后端哪些参数要传过去，code和iv是必须要传的
            },
            fail(error) {
              reject(error);
            }
          })
        }
      }
    })

看文档https://developers.weixin.qq.com/miniprogram/dev/api/open-api/login/wx.login.html