server.js

const express = require('express')
require('dotenv').config()
const app = express()
const jwt = require('jsonwebtoken')

const posts = [
    {
        username: "Zulqadar",
        title: "Post 1"
    },
    {
        username: "Jim",
        title: "Post 2"
    }
]

app.use(express.json())

app.get('/posts', authenticateToken, (req, res)=>{
    res.json(posts.filter(post => post.username === req.user.name));
})

function authenticateToken(req, res, next){
    const authHeader = req.headers['authorization']
    const token = authHeader && authHeader.split(' ')[1]
    if(token == null) return res.sendStatus(401)

    jwt.verify(token , process.env.ACCESS_TOKEN_SECRET, (err, user) => {
        if (err) return res.sendStatus(403)
        req.user = user
        next()
    })
}

app.listen(3000)