Split the work on adding Sign in with Apple

Your Go backend serves a web app and an iPhone app, and accounts use email and password today. You are adding Sign in with Apple. Apple lets people hide their real address behind a private relay address, and it sends the user's name only on their first sign-in. When someone deletes their account, Apple requires you to revoke their Apple tokens. You want an agent to build most of it, and the team plans to ship in 3 weeks.

What do you let the agent build, what do you own, and what has to be checked before release?