To auth, or not to auth

As a matter of fact, implementing authentication and/or authorization logic isn't mandatory for most web-based applications or services; there are a number of websites that still don't do that, mostly because they serve contents that can be accessed by anyone at any time. This used to be pretty common among most corporate, marketing, and informative websites until some years ago; that was before their owners learned how important it is to build a network of registered users and how much these loyal contacts are worth nowadays.

We don't need to be experienced developers to acknowledge how much the WWW has changed in the last few years; each and every website, regardless of its purpose, has an increasing and more or less legitimate interest in tracking their users nowadays, giving them the chance to customize their navigation experience, interacting with their social networks, collecting email addresses, and so on. None of the preceding can be done without an authentication...