Any developer who has built their own membership system knows the feeling: authentication and authorization look simple at first, then slowly grow into a monster. In the beginning it seems like "email + bcrypt password + JWT" is all you need, but soon the demands pile up one after another — password policies, password-reset emails, MFA, social login (Google, Facebook, Apple), enterprise SSO (SAML, Okta, AD), device trust, threat detection, login attempt throttling, token refresh, refresh-token rotation, GDPR consent management, session expiry. The result is that your homegrown auth code ends up more complex than your payment system, and over 70% of security incidents blow up right here.