Best Practices and Advanced Security

You now have an application where identities are verified, passwords are properly hashed, and access is controlled. That's necessary, but it isn't sufficient. The incidents you read about almost never begin with "the attacker broke the authentication." They begin with an Actuator endpoint left open, an API key in a public repository, a three-year-old library, or an exception stack trace displayed in production that revealed the server's full path.

These flaws have one thing in common: none of them is an application code flaw. They are flaws of configuration, operations, and dependency hygiene. OWASP classifies them separately, in fact: "security misconfiguration" and "vulnerable and outdated components" are two distinct categories in its top ten risks list.

This final lesson therefore brings together the elements that don't belong to any of the previous ones but that determine how robust the system really is: the headers the browser must receive, how to enforce HTTPS without causing a redirect loop, rate limiting, useful logging (and the kind of logging that creates a leak of its own), secrets management, and dependency monitoring.