Error: Failed to serialize user into session || This error is coming while I am trying to log in - express

Question

I got a problem with the Passport.js module and Express.js.
This is my code and I just want to use a hardcoded login for the first try.
I always get the message:
I searched a lot and found some posts in stackoverflow but I didnt get the failure.
Code of my app.js
require('dotenv').config()
const express = require('express')
const bodyParser = require('body-parser')
const ejs = require('ejs')
const mongoose = require('mongoose')
const session = require('express-session')
const passport = require('passport')
const passportLocalMongoose = require('passport-local-mongoose')
const app = express();
const port = process.env.PORT
app.use(express.static('public'))
app.set('view engine','ejs')
app.use(bodyParser.urlencoded({extended:true}))
app.use(session({
secret: process.env.SECRET_KEY,
resave: false,
saveUninitialized: false,
}))
app.use(passport.initialize())
app.use(passport.session())
mongoose.connect("mongodb://localhost:27017/userDB")
const userSchema = new mongoose.Schema({
username: String,
password: String,
})
userSchema.plugin(passportLocalMongoose)
const User = new mongoose.model("User",userSchema)
passport.use(User.createStrategy())
passport.serializeUser(User.serializeUser())
passport.deserializeUser(User.deserializeUser())
//Home Route
app.get('/',(req,res)=>{
res.render('home')
})
//Login Route
app.route('/login')
.get((req,res)=>{
res.render('login')
})
.post((req,res)=>{
const user = new User({
username: req.body.username,
password: req.body.password
});
req.login(user, function(err){
if (err) {
console.log(err);
} else {
passport.authenticate("local")(req, res, function(){
res.redirect("/secrets");
});
}
});
})
//Register route
app.route('/register')
.get((req,res)=>{
res.render('register')
})
.post((req,res)=>{
User.register({username: req.body.username}, req.body.password,(err,user)=>{
if(err){
console.log(err);
res.redirect('/register')
}
else{
passport.authenticate("local")(req,res,()=>{
res.redirect("/secrets")
})
}
})
})
app.route('/secrets')
.get((req,res)=>{
res.set('Cache-Control', 'no-store');
if(req.isAuthenticated()){
res.render("secrets")
}
else{
res.redirect("/login")
}
})
app.listen(port,()=>console.log("server started at port "+port))
But its giving this error:
Error: Failed to serialize user into session
at pass (D:\CODING\WEB\Web-Development-Series\Secrets+-+Starting+Code\Secrets - Starting Code\node_modules\passport\lib\authenticator.js:278:19)
at serialized (D:\CODING\WEB\Web-Development-Series\Secrets+-+Starting+Code\Secrets - Starting Code\node_modules\passport\lib\authenticator.js:283:7)
at D:\CODING\WEB\Web-Development-Series\Secrets+-+Starting+Code\Secrets - Starting Code\node_modules\passport-local-mongoose\index.js:212:7
at pass (D:\CODING\WEB\Web-Development-Series\Secrets+-+Starting+Code\Secrets - Starting Code\node_modules\passport\lib\authenticator.js:291:9)
at Authenticator.serializeUser (D:\CODING\WEB\Web-Development-Series\Secrets+-+Starting+Code\Secrets - Starting Code\node_modules\passport\lib\authenticator.js:296:5)
at SessionManager.logIn (D:\CODING\WEB\Web-Development-Series\Secrets+-+Starting+Code\Secrets - Starting Code\node_modules\passport\lib\sessionmanager.js:14:8)
This problem is occuring only in case of login. register is working fine.

Answer 1

This error means passport is not able to hash (serialize) your users. Try to implement your own User.serializeUser() function using the user's _id.