Most Next.js authentication tutorials teach you how to build the plumbing. This one skips that. You don't need to write session logic, token exchange, or JWT verification yourself — and you definitely shouldn't. You need to know where auth lives in a Next.js app, how the App Router changes things, and how to ship it fast without painting yourself into a corner.
A production Next.js app needs session management that survives page refreshes, protected routes that redirect unauthenticated users without flicker, API endpoints that reject requests without a valid token, Server Actions that verify identity before running any business logic, and a sign-in/sign-out flow that handles the OAuth/OIDC roundtrip.
Let's go through each one.
Where Auth Lives in Next.js App Router
Next.js 13+ separates your code into two runtimes: server and client. Auth decisions should happen on the server. If you're checking auth state in a client component to decide what to render, you're doing it in the wrong place — there will be a flash of unauthenticated content before the check resolves.
