How logins work

You sign in to things dozens of times a week, so logins feel ordinary. But when you build one, a lot of words arrive at once: authentication, sessions, cookies, tokens, proxies, policies. Students in earlier cohorts said this was the moment the back end stopped making sense. Not because any one idea is hard, but because nobody showed how they fit together.

So this lesson builds nothing. It gives you one clear picture of a login, start to finish, using a wedding, a wristband and a guest list. Every lesson after this one adds a real piece to that picture. When something goes wrong later, you'll know which piece to look at.