How would you use edge functions (Cloudflare Workers, Vercel Edge) to handle authentication, personalisation, and A/B testing without a full origin server round-trip?

Imagine you have a magic mailbox at the corner of your street. When you send a letter, a tiny helper inside reads it and can change the color of the stamp or add a sticker before it goes to the big post office. Edge functions are like those tiny helpers—they work super fast near you, so you don't have to wait for the big post office to do everything.