MEAN App error expected object

Question

I am trying to code a mean authentication app. Right now i can create user in mongodb via postman but when i try to authenticate it,if it has wrong username or password it gives proper feedback,wrong password etc, but if it matches correct username and password on database, server shutdowns, it doesnt gives any feedback on postman and it gives the following error on server terminal:

(node:11262) DeprecationWarning: Mongoose: mpromise (mongoose's 
default promise library) is deprecated, plug in your own promise 
library instead: http://mongoosejs.com/docs/promises.html
/home/cagdas/Desktop/basictest/node_modules/jsonwebtoken/sign.js:90
throw err;
^

Error: Expected object
    at validate 
(/home/cagdas/Desktop/basictest/node_modules/jsonwebtoken
/sign.js:35:11) at Object.module.exports [as sign] 
(/home/cagdas/Desktop/basictest/node_modules/jsonwebtoken
/sign.js:101:7) at User.comparePassword 
(/home/cagdas/Desktop/basictest/routes/users.js:40:26)
at bcrypt.compare (/home/cagdas/Desktop/basictest/models/user.js:52:6)
at 
/home/cagdas/Desktop/basictest/node_modules/bcryptjs/dist
/bcrypt.js:297:21
at /home/cagdas/Desktop/basictest/node_modules
/bcryptjs/dist/bcrypt.js:1353:21
at Immediate.next (/home/cagdas/Desktop/basictest/node_modules
/bcryptjs/dist/bcrypt.js:1233:21)
at runCallback (timers.js:672:20)
at tryOnImmediate (timers.js:645:5)
at processImmediate [as _immediateCallback] (timers.js:617:5)

This is my code: app.js:

const express = require('express') ;
const path = require('path');
const bodyParser = require('body-parser');
const cors = require('cors');
const passport = require('passport');
const mongoose = require('mongoose');
const config = require('./config/database');


// Connect to Database
mongoose.connect(config.database, { useMongoClient: true });


// On Connection
mongoose.connection.on('connected', () => {
console.log('Connected to database '+config.database);
});

// On Error
mongoose.connection.on('error', (err) =>{
console.log('Database error: '+err);
});

const app = express();

const users = require('./routes/users');

// Port Number
const port = 3000;

// Cors Middleware
app.use(cors());

// Set Static Folder
app.use(express.static(path.join(__dirname, 'public')));

// Body Parser Middleware
app.use(bodyParser.json());

// Passport Middleware
app.use(passport.initialize());
app.use(passport.session());

require('./config/passport')(passport);

app.use('/users', users);

// Index Route
app.get('/', (req, res) => {
res.send('Invalid Endpoint');
});

// Start Server
app.listen(port, () => {
console.log('Server started on port '+port);    
});

users.js:

const express = require('express');
const router = express.Router();
const passport = require('passport');
const jwt = require('jsonwebtoken');
const User = require('../models/user');
const config = require('../config/database');

// Register
router.post('/register', (req, res, next) => {
let newUser = new User({
    name: req.body.name,
    email: req.body.email,
    username: req.body.username,
    password: req.body.password
});

User.addUser(newUser, (err, user) =>{
    if(err){
        res.json({success: false, msg:'Failed to register user'});
    } else {
        res.json({success: true, msg:'User registered'});
    }
});
});

// Authenticate
router.post('/authenticate', (req, res, next) => {
const username = req.body.username;
const password = req.body.password;

User.getUserByUsername(username, (err, user) => {
    if(err) throw err;
    if(!user){
        return res.json({success: false, msg: 'User not found'});
    }

    User.comparePassword(password, user.password, (err, isMatch) => {
        if(err) throw err;
        if(isMatch){
            const token = jwt.sign(user, config.secret, {
                expiresIn: 86400 // 1 day
            });

            res.json({
                success: true,
                token: 'JWT ' +token,
                user: {
                    id: user._id,
                    name: user.name,
                    username: user.username,
                    email: user.email
                }
            });
        } else {
            return res.json({success: false, msg: 'Wrong Password'});
        }
    });
})

});

// Profile
router.get('/profile', (req, res, next) => {
res.send('PROFILE');
});

module.exports = router;

database.js:

module.exports = {
    database: 'mongodb://localhost:27017/basictest',
    secret: '123456789'
}

user.js:

const mongoose = require('mongoose');
const bcrypt = require('bcryptjs');
const config =require('../config/database');

// User Schema
const UserSchema = mongoose.Schema({
name: {
    type: String
},
email: {
    type: String,
    required: true
},
username: {
    type: String,
    required: true
},
password: {
    type: String,
    required: true
}
});


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


module.exports.getUserById = function(id, callback){
User.findById(id, callback);
}


module.exports.getUserByUsername = function(username, callback){
const query = {username: username}
User.findOne(query, callback);
}

module.exports.addUser = function(newUser, callback){
bcrypt.genSalt(10, (err, salt) => {
    bcrypt.hash(newUser.password, salt, (err, hash) => {
        if(err) throw err;
        newUser.password = hash;
        newUser.save(callback);
    });
});
}


module.exports.comparePassword = function(candidatePassword, hash,      
callback){
bcrypt.compare(candidatePassword, hash, (err, isMatch) => {
    if(err) throw err;
    callback(null, isMatch);
});
}

passport.js

const JwtStrategy = require('passport-jwt').Strategy;
const ExtractJwt = require('passport-jwt').ExtractJwt;
const User = require('../models/user');
const config = require('../config/database');


module.exports = function(passport){
let opts = {};
opts.jwtFromRequest = ExtractJwt.fromAuthHeaderWithScheme('jwt');
opts.secretOrKey = config.secret;
passport.use(new JwtStrategy(opts, (jwt_payload, done) => {
    User.getUserById(jwt_payload._id, (err, user) => {
        if(err){
            return done (err, false);
        }
        if(user){
            return done(null, user);
        } else {
            return done(null, false);
        }
    });
}));
}

Answer 1

Solution - not user only { data: user }

const token = jwt.sign({data: user}, config.secret, {
    expiresIn: 604800 // 1 week
});