My app.js script

var express_session = require('express-session');

var session = express_session({
  secret: 'secretkey',
  resave: true,
  saveUninitialized: true,
  cookie: { maxAge: 60 * 60 * 1000 },
});

var indexRouter = require('./routes/index');
var usersRouter = require('./routes/users');

var app = express();

// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'pug');

app.use(cookieParser('secretkey'));
app.use(session);
app.use(logger('dev'));
app.use(fileUpload());
app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(express.static(path.join(__dirname, 'public')));

app.use('/', indexRouter);
app.use('/users', session, usersRouter);

// catch 404 and forward to error handler
app.use(function(req, res, next) {
  next(createError(404));
});

// error handler
app.use(function(err, req, res, next) {
  // 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');
});

module.exports = app;

My users.js script

var express = require('express');
var router = express.Router();

router.get('/enter', function(req, res, next) {
    req.session.user = req.query.username;
    res.redirect('/users/login');
});

module.exports = router;

But req.session is undefined TypeError: Cannot set properties of undefined (setting 'user') I placed app.use(session) before routes, but still don`t work. Tried to add session in app.use('/', session, indexRouter) - not work.

/// UPDATE I changed my indexRouter, now its works!!!!:

var express = require('express');
var router = express.Router();

var express_session = require('express-session');

var session = express_session({
  secret: 'secret',
  resave: true,
  saveUninitialized: true,
  cookie: { maxAge: 24 * 60 * 60 * 1000 },
});
router.use(session);

router.get('/', function(req, res, next) {
  if(req.session && req.session.user){
    res.render('index', { title: 'Adviser', user: req.session.user });
  } else {
    res.redirect('/users/login');
  }
});

module.exports = router;

Thanks Heiko Theißen