app_session.js

var express = require('express');
var session = require('express-session');
var bodyParser = require('body-parser');
var app = express();
app.use(bodyParser.urlencoded({ extended: false}));

app.use(session({
  secret: '1sad%@f1s5d@%1fs3d13s%d1',
  resave: false,
  saveUninitialized: true
}));

app.get('/auth/logout', function(req, res){
  delete req.session.displayName;
  res.redirect('/welcome');
});

app.get('/welcome' , function(req, res){
  if(req.session.displayName){
    res.send(`
      <h1>Hello, ${req.session.displayName}</h1>
      <a href="/auth/logout">logout</a>
      `);
  } else {
    res.send(`
      <h1>Welcome</h1>
      <a href="/auth/login">Login</a>
      `)
  }
})

app.post('/auth/login', function(req, res){
  var user = {
    username:'egoing',
    password:'111',
    displayName:'Egoing'
  };
  var uname = req.body.username;
  var pwd = req.body.password;
  if(uname === user.username && pwd === user.password){
    req.session.displayName = user.displayName;
    res.redirect('/welcome');
  } else {
    res.send('Who are you? <a href="/auth/login">login</a>');
  }
});

app.get('/auth/login', function(req, res){
  var output = `
  <h1>Login</h1>
  <form action="/auth/login" method="post">
    <p>
      <input type="text" name="username" placeholder="username">
    </p>
    <p>
      <input type="password" name="password" placeholder="password">
    </p>
    <p>
      <input type="submit">
    </p>
  </form>
  `;
  res.send(output);
});

app.get('/count', function(req, res){
  if(req.session.count){
    req.session.count++;
  } else {
    req.session.count = 1;
  }
  res.send('count :'+req.session.count);
})

app.listen(3003, function(){
  console.log('Connected 3003 port !!!');
});