You've covered a lot of ground in this chapter, looking at not only user authentication in Express applications, but also microservices development.
Specifically, you covered session management in Express, using Passport for user authentication—including Twitter/OAuth, using router middleware to limit access, creating a REST service with Restify, and when to create a microservice. We've even used an encryption algorithm to ensure that we only store encrypted passwords.
Knowing how to handle login/logout, especially OAuth login from third-party services, is an essential skill for web application developers. Now that you've learned this, you'll be able to do the same for your own applications.
In the next chapter, we'll take the Notes application to a new level with semi-real-time communication between application users. To do this, we'll write some browser-side JavaScript and explore how the Socket.io package can let us send messages between...