Laravel UI + Passport + Nuxt sidebase + guards

I have installed Laravel (as API) with Passport and Laravel UI to allow login from a Nuxt frontend website with Sidebase. Sign in works fine this way.

However, I'd like my API to manage another Nuxt backend website with admin users table. So I created a web-admin guard and a web-admins provider in auth.php.

How to make the backend use the web-admin guard when logging in? Maybe by changing something in LoginController.php?