Backend authenticate:

const express = require('express');
const router = express.Router();
const jwt = require('jsonwebtoken');
const moment = require('moment');
const Users = require('../helpers/userLookup');
const userService = new Users();

module.exports = {
    authenticate
};
/**
 * decodes a basic auth string to authenticate a user
 * @param  {object} req the recieved request body
 * @param  {object} res response body to send back
 */
function authenticate(req, res) {
    let creds = decode(req.headers.authorization);
    if (!creds.password) {
        res.status(401).json({
            error: 'Could not log in. One or more fields were missing.'
        });
    } else {
        validateUser(creds).then((result) => {
            let token = jwt.sign(result, 'defInItelyNotaSecReT', { expiresIn: '8h' });
            res.status(200).json({
                message: 'Login successful!',
                user: result,
                expires: moment().add(8, 'h').utc(),
                token: token
            });
        }).catch((error) => {
            if (error.serviceFailed) {
                res.status(500).json(error);
            } else {
                res.status(401).json(error);
            }
        });

    }
}
/**
 * validates that a user with the given information exists in the database
 * @param  {object} creds user information decoded from the basic auth string
 */
function validateUser(creds) {
    return new Promise((resolve, reject) => {
        userService.retrieveByQuery({
            email: creds.email
        }).then((users) => {
            if (!users[0]) {
                reject({
                    message: 'Could not log in. The email address you entered is not a valid user account. Please try again.'
                });
            } else if (users[0].password == creds.password) {
                resolve(users[0]);
            } else {
                reject({
                    message: 'Could not log in. The password you entered is incorrect.'
                });
            }
        }).catch((error) => {
            reject({
                serviceFailed: true,
                message: error
            });
        });
    });
}

/**
 * decodes a given basic auth string
 * @param  {object} header the header field from post endpoint's request body
 */
function decode(header) {
    let auth = header.split(' ');
    let buffer = Buffer.from(auth[1], 'base64').toString();
    let creds = buffer.split(':');
    if (!creds[1]) {
        creds[1] = false;
    }
    //The following allows passwords (but not email addresses!) to contain the ":" character.
    for (let i = 2; i < creds.length; ++i) {
        creds[1] += ':' + creds[i];
    }
    return {
        email: creds[0],
        password: creds[1]
    };
}