Working with Node/JS and Express for Services
At The Shop, we are using a completely different platform than I've used in the past - Node/JS and Express as well as Platter, for a back-end database. It's been a steep learning curve for me, but I have to say today was a nice day where I really started to feel like I was getting the handle on the tools. What has really exciting to me with Express is the ease with which I can build middleware to insert into the calling stack.
For ring middleware, in Clojure, it's not horrible, but it's not trivial to understand the calling order, and the passing of the handler to all the middleware. In Express, it's far simpler - you simply have a function that takes the request, the response, and the next in the line of the calling stack, and that's it. You can augment the request, and that's basically what a lot of middleware is about - adding authentication tokens, looking up permissions, etc. It's all adding to the request to be used in the simpler endpoint routes.
When working with Passport for the authentication framework, it's great that it fits in with Express so well, but one of the issues that I ran into today was that the middleware added to the top-level Express app would be executed before the Passport authentication middleware that was in place on each individual endpoint. It makes sense, not all endpoints need authentication, so adding that with Passport would naturally be done after the top-level middleware. But that makes some of the middleware I'd written unfunctional.
The Passport authentication scheme can be set up to easily add the user object to the Express request, and then for all endpoints, it's "Just There". I had expected to add middleware that would take that user and use it to look up other attributes and data to add to the request as well. But if the middleware I'd written was placed at the top-level, then it wouldn't have the user object on the request, and so it'd never work.
The solution was so elegant, I'm convinced that this had to be anticipated by the Express developers. 🙂 Each of the routes wired into the Express app takes a path and a router:
app.use('/login', loginRouter) app.use('/company', companyRouter)
and when you add in the Passport support for JWT authentication with a Bearer token, you get something like:
app.use('/login', loginRouter) app.use('/company', passport.authenticate('jwt', { session: false }), companyRouter)
where the /login endpoint is not protected by the JWT, and the /company endpoint is. This seemed like a very late stage to put in the Passport middleware, but as it turns out, Express can handle an array, or a list of middleware in the use() function. So we can say:
const authStack = [ passport.authenticate('jwt', { session: false }), tenantMiddleware, accountMiddleware, ] app.use('/login', loginRouter) app.use('/company', authStack, companyRouter)
where the authStack is the additional middleware for the individual routes, and it's handled in the order it appears in the array.
And it works like a champ. Just amazing, that we can create different stacks of middleware and then as long as we layer them properly, we can set up an amazing diversity of middleware. For this, it's great that we can group the authentication-focused middleware into an array, and then easily drop that on the endpoints that need it.
Very slick. 🙂