JWT vs Server Sessions: The Ultimate Guide

"We use JWT because it is modern." This is a bad reason.

Server Sessions (Stateful)

1. User logs in.
2. Server creates a Session ID (random string), stores it in Redis/DB.
3. Sends ID as Set-Cookie (HttpOnly).
4. Revocation: Easy! Just delete it from Redis. User is logged out instantly.

JWT (Stateless)

1. User logs in.
2. Server signs a JSON token with a secret.
3. Sends token to client.
4. Server forgets it!
5. Client sends token back. Server verifies signature.

The Problem: You cannot revoke a JWT. If it is stolen, the attacker has access until it expires. Fix: Short expiry (15 min) + Refresh Tokens (stored in DB). Wait... if you store Refresh Token in DB, aren't you just doing Sessions with extra steps?

When to use What?

Use Sessions (Cookies) if:

• You are a standard Web App (Next.js, Rails, Django).
• Immediate revocation is important (Billing, Admin panels).

Use JWT if:

• You have Microservices (Auth service issues token, others verify).
• Mobile App is the client (Cookies are hard on mobile).

Best Practice

For a typical Next.js app: Use NextAuth.js. It handles sessions (via database) or JWTs automatically. Don't roll your own crypto.