In all of our previous applications, we referred to the application's users as persons who can interact with the software and not necessarily users with a unique user identity persisted in our database. In real-life applications, these types of users are often called visitors since they can just visit the application without leaving behind any personal information. There are many scenarios where we can have users using the app without registration. Typically, we would use some type of software analytics to track the number of visitors, but at some point, we may need to have them registered. Let's discuss some example cases where we need to maintain user accounts' functionality in our applications.

First, let's look at monetization. Users will be provided with the option to pay for services provided by the app, and we need to register them securely with their payment information. Then we have advertisers paying for putting advertisements in our application, and they...