Check citizen exists

HEAD /api/core/users/{sub} → FindUserUseCase

A lightweight existence check, so the app or front-end can tell whether an Auth0 sub is already provisioned — e.g. to decide between the registration and the normal flow before requesting an OTP. Being a HEAD request it returns no body, only the status code: 200 OK if the user exists, 404 Not Found otherwise.

The result is cached in citizenExists keyed by sub; the entry is invalidated on sign-in and delete.

Inputs

HEAD /api/core/users/{sub} — no body.

Outputs

• 200 OK — the user exists (no body).
• 404 Not Found — it does not exist (no body).

Sequence — microservices

Sequence — monolith