Integrations
Step-by-step guides with copy-ready code. Any backend works: it is one HTTPS request, see the docs.
Next.js
Route handler or server action: one call before you create the user.
Supabase
Check before supabase.auth.signUp() and keep the result where users cannot change it.
Clerk
Check each new user once on the server and keep the result in publicMetadata.
Firebase
A blocking function checks every signup before the user is created.
FastAPI
One call in your Python signup route, before you create the user.
Better Auth
A small plugin checks every new user before Better Auth creates it.
Express
One call in your signup route, before you create the user.