"Security isn't a feature you add at the end. It's the foundation you build everything else on top of."
Introduction: How Does a Website Know Who You Are?
Think about the last time you logged into a website. You typed your email and password, clicked a button, and suddenly the app knew who you were — your name appeared, your data loaded, your settings were right.
That moment involves several invisible systems working together. How did the server verify your password without storing it somewhere a hacker could read? How did it decide what you're allowed to see? How does "Login with Google" work without giving Google your password?
These questions touch on the core of application security. This guide answers all of them — from the fundamentals of password storage through modern authentication architectures used by the world's largest platforms.
