Creating JWT

app.js

var express = require('express');
var app = express();
const expressjwt = require('express-jwt')
const jsonwebtoken = require('jsonwebtoken');

// this will verify the token before going to actual requested route (middleware)
// except the "/login" route every request needs token in header which will look like "Authorization:Bearer eyJh..........." refer image in story
app.use(expressjwt({secret: "some key"}).unless({path: ['/', '/login']}))

// login user routing 
app.post('/login', (req, res) => {
  // creating token with user data "{username: req.body.username}"
  const token = jsonwebtoken.sign({username: req.body.username}, "some key");
  res.status(200).send(token);
})

// on user request "/getData"
app.get('/getData', (req, res) => {
    // to retrieve same data which we haved saved during token generation
   jsonwebtoken.verify(req.get('Authorization').replace("Bearer ", ""), "some key", {
    ignoreExpiration: true
  }, (err, data) => {
    res.status(200).send(data);
  })
})

// to write you own error message on wrong token 
app.use(function (err, req, res, next) {
  // this is for custom message on wrong/no token 
  if (err.name === "UnauthorizedError") {
    res.status(401).send("No token")
  } else {
    // set locals, only providing error in development
    res.locals.message = err.message;
    res.locals.error = req.app.get('env') === 'development' ? err : {};

    // render the error page
    res.status(err.status || 500);
    res.render('error');
  }
});