Authentication in Express Middleware - node.js

Question

I'm a little new to this. I have REST API made with Node.js and Express.js. Some routes have authentication middleware. To use those routes, a header has to be set with the user's auth token which gets verified. I have been doing this with no problem with static sites using local storage. I'm making my first dynamic site now (using Express) and for certain routes I have middleware that loads all the data I need to display the page. How do I access and use auth tokens now that I don't have local storage's help?
EDIT(for clarification):
So here is one of my api routes that fetches all transactions from a database(mongoDB).
app.get('/transactions', authenticate, (req, res) => {
Transaction.find().then((transaction) => {
res.send({transaction});
}, (e) => {
res.status(400).send();
});
});
This is the authentication middleware that gets run.
var authenticate = (req, res, next) => {
var token = req.header('x-auth');
User.findByToken(token).then((user) => {
if (!user) {
return Promise.reject();
}
req.user = user;
req.token = token;
next();
}).catch((e) => {
res.status(401).send();
});
};
Now on my express webserver, I have a following route, where I use getTransactions to fetch all my data. (which I display with handlebars)
router.get('/orders', getTransactions, (req, res) => {
res.render('orders.hbs', {
transaction: req.transactions.data.transaction
});
});
and this is the middleware
var getTransactions = (req, res, next) => {
axios.get('https://serene-wave-28270.herokuapp.com/transactions')
.then((response) => {
req.transactions = response;
console.log(req.transactions.data.transaction);
next();
}).catch((e) => {
console.log(e);
})
}
So when I was just making a static site without using express as a webserver, I would just have the user sign in and save the auth token in local storage. Also, I should note that the first two blocks are from my api, and the bottom two from webserver, both hosted separately on Heroku. I'm not sure if that's standard design so I thought I should mention it.

Answer 1

There's not a whole lot of detail in your question for exactly what you're trying to do, but I can explain the general concepts available to you in Express:
The usual scheme for Express is to authenticate the user initially and then set a session cookie that indicates that user has been authenticated. Since the cookie is automatically stored by the browser and then automatically sent from the browser to the server with every request, you will have that cookie which the server can then use to identify a server-side session and then you can use any info you want from the session (user identify or other state you store in the session object) when creating pages or responding to API requests for that user.
The NPM module express-session handles much of this work for you as it will automatically create a session object, a session cookie and hook the two together on every request.
If, on the other hand, you already have an auth token in the client and you just want that to be automatically communicated to the server with every request, then you can just put that auth token into a cookie and have the server look for it in the cookie on each request. You can even make it a bit more secure by setting the cookie to HttpOnly so that the auth token cannot be accessed from client-side Javascript (this will not affect the server's ability to access it).

Answer 2

There is not much detail in your question but here are a few thoughts.
You can either use cookies (as detailed by #jfriend00 below) or use the requests' headers to check for a valid authorization token (which I describe below)
In Express you can access the headers through req.headers so you can just write a middleware that you will call before your current middleware loading all the data to ensure that the user is authorized to continue (calling next() to call the next middleware) or using a custom Error type to flag the authentication error if he is not (calling next(err) to skip all the other middleware and jump to your error middleware)
For example (assuming you have a subclass of Error named AuthorizationError defined somewhere):
const express = require('express');
const AuthorizaztionError = require('<some path>');
const app = express();
function checkAuthTokenMiddleware(req, res, next) {
if (req.headers && req.headers.authorization) {
let token;
const parts = req.headers.authorization.split(' ');
if (parts.length == 2) {
const [scheme, credentials] = parts;
if (/^Bearer$/i.test(scheme)) { // or any other scheme you are using
token = credentials;
}
if (token === undefined) {
// access token - missing
return next(new AuthorizationError(
"Invalid access token.", // error_description
"invalid_token" // error
));
}
// add something here to ensure the token is valid
return next();
}
} else {
// No authorization header => invalid credentials
return next(new AuthorizationError(
"Authorization header required.", // error_description
"invalid_request" // error
));
}
}
// Add this in your route declaration
app.use(
"/auth/test",
checkAuthTokenMiddleware,
function(req, res, next) {
// do something
}
);
// this must come last
app.use(function errorMiddleware(err, req, res, next) {
// return something
if (err instanceof AuthenticationError) {
// do something for example
res.status(401).send(err.error_description);
} else {
// generic error handling, for example
res.status(500).send("Error "+err);
}
})
// ...