The Identity Stack Explained — Who Are You, and What Can You Do?
Understanding authentication vs authorization and the full identity stack that powers every modern application
Every application you've ever logged into answers two fundamental questions. The first: "Who are you?" The second: "What are you allowed to do?" These sound similar, but they're completely different problems with completely different solutions. Confusing them is one of the most common mistakes developers make — and one of the most dangerous.
If you've been building apps with AI tools, your agent has probably set up some form of authentication for you. Maybe Clerk, maybe NextAuth, maybe a hand-rolled JWT system. But do you actually understand what's happening under the hood? Because when something breaks in your auth system — and it will — "the AI set it up" isn't going to help you debug it.
Let's build a mental model of the entire identity stack from the ground up.
Authentication v
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