passport-local-mongoose authenticate example

auth.js

//USER SCHEMA

const mongoose = require('mongoose');
const passportLocalMongoose = require('passport-local-mongoose');

module.exports = (function () {
  
    const userSchema = mongoose.Schema({
        username: String,
        password: String,
        displayName: { type: String, unique: true, required: true },
        created: {
            type: Date, default: Date.now
        },
        updated: Date,
        isAdmin: { type: Boolean, default: false }
    });

    userSchema.plugin(passportLocalMongoose);

    const User = mongoose.model('User', userSchema);

    return User;
}());

//THE AUTH LOGIC FOR INSIDE MIDDLEWARE OR ENDPOINTS

const authenticate = User.authenticate();
authenticate(req.user.username, update.newPassword, (err, result) => {
    if (err) {
        res.flash('danger', 'There was a problem updating your password.');
        res.redirect(`/users/${req.user._id}`);
    } else {
        if (!result) {
            res.flash('danger', 'Incorrect old password.');
            res.redirect(`/users/${req.user._id}`);
        } else {
            res.send('Authenticated');
        }
    }    
});