index.js

const express = require('express');
const users = require('./users');

const app = express();
const PORT = process.env.PORT || 5000

const authenticate = ({ username, password }) => {
  const user = users.find((user) => {
    return user.username === username
  })
  if (user) {
    if (user.password === password) {
      return user
    }
  }
}

const checkRole = (req, res, next) => {
  if (req.role === "admin") {
    next()
  } else {
    res.status(403).send('you\'re not authorized')
  }
}

app.use(express.json())

app.use((req, res, next) => {
  const user = authenticate(req.body)
  if (user) {
    req.role = user.role
    next()
  } else {
    res.status(403).send('you\'re not authenticated')
  }
})

app.post('/login', checkRole, (req, res) => {
  res.send('welcome user! 😊')
})

app.listen(PORT, () => console.log(`listening on port ${PORT}`))