[keycloak-user] Disallow Join via OAuth?

I don't expect this is possible, but does anyone know whether one can prevent new account creation when Identity Brokering with Facebook and Google while still allowing sign-in? We are attempting to migrate our legacy IDM solution to Keycloak slowly and wish, for the time being, for all new account creation to still go through the legacy app. We have HAProxy in front of Keycloak. Is there a way to redirect users attempting to join via Facebook or Google to our legacy join page?