Can't use passport.authenticate('local') - node.js

Question

I posted question here cuz I my passport.authenticate('local') shows nothing, so I cannot use login function. I can activate singup api that I created, but somehow I cannot use my login api that I created as well.
Here is my code below.
var createError = require('http-errors');
var express = require('express');
var ejsMate = require('ejs-mate');
var path = require('path');
var cookieParser = require('cookie-parser');
var logger = require('morgan');
var config = require('./config')
var passport = require('passport')
// var session = require('express-session')
var homeRouter = require('./routes/home');
var usersRouter = require('./routes/users');
const mongoose = require('mongoose')
const url = config.mongoUrl
const connect = mongoose.connect(url)
connect.then((db) => {
console.log('Connected correctly to server')
}, (err) => {console.log(err)})
var app = express();
// view engine setup
//GET, POST, DELETE, PUT
app.engine('ejs', ejsMate)
app.set('view engine', 'ejs');
app.set('views', path.join(__dirname, 'views'));
app.use(logger('dev'));
app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(passport.initialize())
//localhost:3000/
app.use('/', homeRouter);
//localhost:3000/users
app.use('/users', usersRouter);
app.use(express.static(path.join(__dirname, 'public')))
// 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;
var express = require('express');
const bodyParser = require('body-parser')
var User = require('../models/users')
var passport = require('passport')
var authenticate = require('../authenticate')
var router = express.Router();
router.use(bodyParser.json())
/* GET users listing. */
router.get('/', (req, res, next) => {
console.log("HAHA")
User.find({})
.then((Users) => {
res.statusCode = 200
res.setHeader('Content-Type', 'application/json')
res.json(Users)
}, (err) => next(err))
.catch((err) => next(err))
});
router.post('/signup', (req, res, next) => {
User.register(new User({username: req.body.username}),
req.body.password, (err, user) => {
if(err) {
res.statusCode = 500;
res.setHeader('Content-Type', 'application/json');
res.json({err: err});
}
else {
if(req.body.firstname)
user.firstname = req.body.firstname
if(req.body.lastname)
user.lastname = req.body.lastname
user.save((err, user) => {
if(err) {
res.statusCode = 500;
res.setHeader('Content-Type', 'application/json');
res.json({err: err});
return;
}
passport.authenticate('local')(req, res, () => {
res.statusCode = 200;
res.setHeader('Content-Type', 'application/json');
res.json({success: true, status: 'Registration Successful!'});
})
})
}
})
});
router.post('/login', passport.authenticate('local'), (req, res) => {
var token = authenticate.getToken({_id: req.user._id});
res.statusCode = 200;
res.setHeader('Content-Type', 'application/json');
res.json({success: true, token: token, status: 'You are successfully logged in!'});
})
router.get('/logout', (req, res, next) => {
console.log(req.session)
if (req.session) {
req.session.destroy();
res.clearCookie('session-id');
res.redirect('/');
}
else {
var err = new Error('You are not logged in!');
err.status = 403;
next(err);
}
});
module.exports = router;
router.post('/login', passport.authenticate('local') ---> show nothing it keep showing me an error
I need some advice and help.