Build the Authentication Boundary Before the Feature

Authentication is not the form where a user types an email. It is the contract that decides who may enter the system, what they are allowed to touch, how long that permission lasts, and how you recover when something goes wrong.

Before a feature ships, define the actors, permissions, session shape, audit trail, and failure states. If you skip this work, every later feature invents its own version of access control.

A good auth boundary is boring in production. Users log in, teams understand permissions, admins can recover accounts, and engineers can reason about data exposure without reading every controller.