Stateful vs Stateless Authentication.
How do you keep users logged in? Sessions stored on the server? Or JSON Web Tokens stored on the client? It's the classic debate of Security vs Scalability.
I am secure. The session ID is just a random string. The data lives on the server. If a user is compromised, I delete the session server-side. Instant revocation.
I am stateless. You don't need to check a database for every request. The data is in the token. I scale across microservices and regions effortlessly.
But you can't be revoked! If a JWT is stolen, it's valid until it expires. You have to implement complex blacklists, which defeats your stateless purpose.
I work everywhere. Mobile apps, SPAs, different domains. Cookies are tricky with CORS. I am just a header: `Authorization: Bearer`.
My cookie is tiny. Your token gets huge with claims. And storing you in LocalStorage is an XSS vulnerability waiting to happen.
For most standard web applications, Server-side Sessions (HttpOnly cookies) are more secure and easier to manage. JWTs are excellent for microservices architectures or mobile apps where centralized session state is a bottleneck.