2 parts, in order.
Home Realm Discovery is a well-understood pattern at the network layer, but moving that routing logic inside Auth0's login flow using Advanced Custom Universal Login opens up some interesting possibilities — and a few unexpected challenges.
In part one we built the Auth0 ACUL screens for multi-tenant routing with a hardcoded lookup. In this post I will replace that with a real Cloudflare Worker backed by Workers KV, move to full email-address routing, handle users who exist across multiple tenants, and add Cloudflare Turnstile bot protection to the login screens.