How to obtain user session_key, openid, unioni in WeChat applet (code)

/**
 * Promise化小程序接口
 */
class Wechat {
  /**
   * 登陆
   * @return {Promise} 
   */
  static login() {
    return new Promise((resolve, reject) => wx.login({ success: resolve, fail: reject }));
  };

  /**
   * 获取用户信息
   * @return {Promise} 
   */
  static getUserInfo() {
    return new Promise((resolve, reject) => wx.getUserInfo({ success: resolve, fail: reject }));
  };

  /**
   * 发起网络请求
   * @param {string} url  
   * @param {object} params 
   * @return {Promise} 
   */
  static request(url, params, method = "GET", type = "json") {
    console.log("向后端传递的参数", params);
    return new Promise((resolve, reject) => {
      let opts = {
        url: url,
        data: Object.assign({}, params),
        method: method,
        header: { 'Content-Type': type },
        success: resolve,
        fail: reject
      }
      console.log("请求的URL", opts.url);
      wx.request(opts);
    });
  };

  /**
   * 获取微信数据,传递给后端
   */
  static getCryptoData() {
    let code = "";
    return this.login()
      .then(data => {
        code = data.code;
        console.log("login接口获取的code:", code);
        return this.getUserInfo();
      })
      .then(data => {
        console.log("getUserInfo接口", data);
        let obj = {
          js_code: code,
        };
        return Promise.resolve(obj);
      })
      .catch(e => {
        console.log(e);
        return Promise.reject(e);
      })
  };

  /**
   * 从后端获取openid
   * @param {object} params 
   */
  static getMyOpenid(params) {
    let url = 'https://xx.xxxxxx.cn/api/openid';
    return this.request(url, params, "POST", "application/x-www-form-urlencoded");
  };
}
module.exports = Wechat;

let wechat = require('./utils/wechat.js');
App({
  onLaunch() {
    this.getUserInfo();
  },
  getUserInfo() {
    wechat.getCryptoData()
      .then(d => {
        return wechat.getMyOpenid(d);
      })
      .then(d => {
        console.log("从后端获取的openid", d.data);
      })
      .catch(e => {
        console.log(e);
      })
  }
})

const request = require("request");
class Ut {

    /**
     * promise化request
     * @param {object} opts 
     * @return {Promise<[]>}
     */
    static promiseReq(opts = {}) {
	return new Promise((resolve, reject) => {
	    request(opts, (e, r, d) => {
		if (e) {
		    return reject(e);
		}
	        if (r.statusCode != 200) {
		    return reject(`back statusCode：${r.statusCode}`);
		}
		return resolve(d);
	    });
	})
    };

};

module.exports = Ut;

router.post("/openid", async (req, res) => {
  const Ut = require("../common/utils");
  try {
    console.log(req.body);
    let appId = "wx70xxxxxxbed01b";
    let secret = "5ec6exxxxxx49bf161a79dd4";
    let { js_code } = req.body;
    let opts = {
      url: `https://api.weixin.qq.com/sns/jscode2session?appid=${appId}&secret=${secret}&js_code=${js_code}&grant_type=authorization_code`
    }
    let r1 = await Ut.promiseReq(opts);
    r1 = JSON.parse(r1);
    console.log(r1);
    res.json(r1);
  }
  catch (e) {
    console.log(e);
    res.json('');
  }
})