Update authorization endpoint for KeyCloak registrations request

[tgermain-impirica]

The OIDC spec indicates ?prompt=create should be appended to the auth request in order to trigger a registration flow. However, KeyCloak doesn't use that prop, and instead has a separate /registrations endpoint that can be used.

The Auth.js flow works perfectly IF I call "signin" and trace the code. I capture the full URL that will be sent to KeyCloak as a sign in request (to /auth). I copy the string, and simply replace /auth with /registrations and the sign up flow works correctly.

Is there any way in auth.js to augment the signIn function and pass in a replacement authorization_url dynamically, or perhaps have auth.js KeyCloak provider automatically replace /auth with /registrations if the prompt=create param is included in the request?