WeChat applet implements user login module server construction

npm init -y

npm install express –save
npm install request --save

npm install nodemon -g

const express = require('express')
const bodyParser = require('body-parser')
const request = require('request')
const app = express()
app.use(bodyParser.json())
const wx = {
  appid: '', // Need to fill in the developer's AppID
  secret: '' // Need to fill in the developer's AppSecret
}

var db = { // simulated database session: {}, // save session information of openid and session_key user: {} // save user records, such as user name, points, etc.}

app.post('/login', (req, res) => {
  var url = 'https://api.weixin.qq.com/sns/jscode2session?appid=' +
  wx.appid + '&secret=' + wx.secret + '&js_code=' + req.body.code +
   '&grant_type=authorization_code'  
  request(url, (err, response, body) => {
     if(){ // The code here determines whether session.openid exists}
     }
     res.json({token: token})
  })
})

if (session.openid) {
      var session = JSON.parse(body)
      // Used to generate token
      var token = 'token_' + new Date().getTime()
      db.session[token] = session 
}

app.listen(3000, () => {
  console.log('server running at http://127.0.0.1:3000')
})

var crypto = require('crypto')

function WXBizDataCrypt(appId, sessionKey) {
  this.appId = appId
  this.sessionKey = sessionKey
}

WXBizDataCrypt.prototype.decryptData = function (encryptedData, iv) {
  // base64 decode
  var sessionKey = new Buffer(this.sessionKey, 'base64')
  encryptedData = new Buffer(encryptedData, 'base64')
  iv = new Buffer(iv, 'base64')

  try {
     // Decryption var decipher = crypto.createDecipheriv('aes-128-cbc', sessionKey, iv)
    // Set automatic padding to true and delete the padding decipher.setAutoPadding(true)
    var decoded = decipher.update(encryptedData, 'binary', 'utf8')
    decoded += decipher.final('utf8')
    
    decoded = JSON.parse(decoded)

  } catch (err) {
    throw new Error('Illegal Buffer')
  }

  if (decoded.watermark.appid !== this.appId) {
    throw new Error('Illegal Buffer')
  }

  return decoded
}

module.exports = WXBizDataCrypt

// Encryption and decryption const crypto = require('crypto');
const WXBizDataCrypt = require('./WXBizDataCrypt')

const express = require('express')
const bodyParser = require('body-parser')
const request = require('request')
const app = express()
app.use(bodyParser.json())

const wx = {
    appid: '',
    secret: ''
}

var db = {
    session: {},
    user: {}
}

app.post('/login', (req, res) => {
    // Note: The appid on the mini program side must use a real account. If a test account is used, a login code error will occur console.log('login code: ' + req.body.code)
    var url = 'https://api.weixin.qq.com/sns/jscode2session?appid=' + wx.appid + '&secret=' + wx.secret + '&js_code=' + req.body.code + '&grant_type=authorization_code'
    request(url, (err, response, body) => {
        console.log('session: ' + body)
        var session = JSON.parse(body)
        if(session.openid) {
            var token = 'token_' + new Date().getTime()
            db.session[token] = session
            if(!db.user[session.openid]) {
                db.user[session.openid] = {
                    credit: 100
                }
            }
        }
        res.json({
            token: token
        })
    })
})

app.get('/checklogin', (req, res) => {
    var session = db.session[req.query.token]
    console.log('checklogin: ', session)
    // Return the Boolean value of whether the user is logged in to the client res.json({
        is_login:session !== undefined
    })
})

app.get('/credit', (req, res) => {
    var session = db.session[req.query.token]
    if(session && db.user[session.openid]) {
        res.json({
            credit: db.user[session.openid].credit
        })
    } else {
        res.json({
            err: 'The user does not exist or is not logged in. '
        })
    }
})

app.post('/userinfo', (req, res) => {
    // Get the session value var session = db.session[req.query.token]
    console.log('session:' + session)
    if(session) {
        // Decrypt encryptedData using appid and session_key
        var pc = new WXBizDataCrypt(wx.appid, session.session_key)
        var data = pc.decryptData(req.body.encryptedData, req.body.iv)
        console.log('After decryption:', data)
        // Check if rawData is correct var sha1 = crypto.createHash('sha1')
        sha1.update(req.body.rawData + session.session_key)
        var signature2 = sha1.digest('hex')
        console.log(signature2)
        console.log(req.body.signature)
        res.json({
            pass: signature2 === req.body.signature
        })
    } else {
        res.json({
            err: 'The user does not exist or is not logged in. '
        })
    }
})

app.listen(3000, () => {
    console.log('server running at http://127.0.0.1:3000')
})

nodemon app.js