Login/Logout/Register using Passport-Local-Mongoose

app.js

var express = require("express"),
    mongoose = require("mongoose"),
    bodyParser = require("body-parser"),
    User = require("./models/user"),
    passport = require("passport"),
    LocalStrategy = require("passport-local"),
    passportLocalMongoose = require("passport-local-mongoose");
    
mongoose.connect("mongodb://localhost:27017/auth_demo_app", { useNewUrlParser: true });    
var app = express();
app.set("view engine","ejs");
app.use(bodyParser.urlencoded({ extended: true }));
app.use(require("express-session")({
    secret:"Miss white is my cat",
    resave: false,
    saveUninitialized: false
}));

app.use(passport.initialize());
app.use(passport.session());

passport.use(new LocalStrategy(User.authenticate()));
passport.serializeUser(User.serializeUser());
passport.deserializeUser(User.deserializeUser());

// ===================
//     ROUTES
// ===================



app.get("/",function(req, res){
   res.render("home"); 
});

app.get("/secret", isLoggedIn, function(req, res){
    res.render("secret");
});

app.get("/register", function(req, res){
    res.render("register");
});

// handeling user sign up
app.post("/register", function(req, res){
    // console.log(req.body.username);
    // console.log(req.body.password);
    User.register(new User({username: req.body.username}), req.body.password, function(err, user){
        if(err){
            console.log(err);
            return res.render("register");
        }
        passport.authenticate("local")(req, res, function(){
            res.redirect("/secret");
        });
    });
});

// Login Form
app.get("/login", function(req, res){
    res.render("login");
});

// Login Logic
// middleware
app.post("/login", passport.authenticate("local",{
    successRedirect: "/secret",
    failureRedirect: "/login"
}), function(req, res){
    
});

// Logout
app.get("/logout", function(req, res){
    req.logout();
    res.redirect("/");
});

// check isLoggedIn
function isLoggedIn(req, res, next){
    if(req.isAuthenticated()){
        return next();
    }
    res.redirect("/login");
}


app.listen(process.env.PORT, process.env.IP, function(){
    console.log("app started!!!")
});

home.ejs

<h1>This is the homepage!</h1>

<li><a href="/register">register!</a></li>
<li><a href="/login">login!</a></li>
<li><a href="/logout">logout!</a></li>

login.ejs

<h1>Login Page</h1>
<form action="/login" method="POST">
    <input type="text" name="username" placeholder="username">
    <input type="password" name="password" placeholder="password">
    <button>Submit</button>
</form>
<li><a href="/register">register!</a></li>
<li><a href="/login">login!</a></li>
<li><a href="/logout">logout!</a></li>

register.ejs

<h1>Sign Up Form</h1>
<form action="/register" method="POST">
    <input type="text" name="username" placeholder="username">
    <input type="password" name="password" placeholder="password">
    <button>Submit</button>
</form>
<li><a href="/register">register!</a></li>
<li><a href="/login">login!</a></li>
<li><a href="/logout">logout!</a></li>

secret.ejs

<h1>Secret page</h1>

<li><a href="/register">register!</a></li>
<li><a href="/login">login!</a></li>
<li><a href="/logout">logout!</a></li>

user.js

var mongoose = require("mongoose");
var passportLocalMongoose = require("passport-local-mongoose");

var UserSchema = new mongoose.Schema({
    username: String,
    password: String
});

UserSchema.plugin(passportLocalMongoose);

module.exports = mongoose.model("User", UserSchema);

userSchema.plugin(passportLocalMongoose); should be added in order for User.authenticate() to work:

'./models/user'

const mongoose = require("mongoose");

const userSchema = new mongoose.Schema({
  username: { type: String, required: true },
  password: { type: String, required: true },
});

const passportLocalMongoose = require("passport-local-mongoose");
userSchema.plugin(passportLocalMongoose);
const user = mongoose.model("user", userSchema);
module.exports = user;