Login Controller for Express Route

login.js

const Promise = require('bluebird');
const bcrypt = require('bcrypt');
const User = require('../models/user');
const { LoginError } = require('../errors');

function checkPassword(password, hash) {
    return Promise.try(() => {
        return bcrypt.compare(password, hash);
    }).then((result) => {
        if (!result) {
            throw new LoginError('invalid password');
        }
    })
    
}

function authenticateUser(username, password) {
    return Promise.try(() => {
        // this will return a single object, not an array. it will also throw if the username is invalid
        return User.findOne({ username }); 
    }).tap((user) => {
        return checkPassword(password, user.password);
    }).then((user) => {
         // return something actually related to the user here?
    })
}

function login(req, res, next) {
    const { username, password } = req.body;
    
    Promise.try(() => {
        return authenticateUser(username, password);
    }).then((user) => {
        res.json({
            message: 'successful login',
            /* add some user data? */
        });
    }).catch(InvalidLogin, (err) => { // catches only instances of InvalidLogin
        return res.status(403).json({ message: 'invalid login' });
    }).catch(next); // everything else goes to global error handler
}

module.exports = login;