[keycloak-user] User registration outside of Keycloak login form

Hi Keycloak users, a strange question for the community ... I have a customer that wants to have SSO but does not want to use the Keycloak registration screens (themed or otherwise) but requires the user to be "logged in" to Keycloak after user registration. My understanding is that to get the SSO magic to work, a user agent must be redirected to the Keycloak server so the KEYCLOAK_SESSION? cookie can be set so that when the user navigates to another SSO enabled site after user registration, they would be identified in the auth flow of this client. Is there any way to create a valid SSO session without using the registration forms of Keycloak server itself? Like doing an XHR request that would create a user registration and also sets the required server side cookies in the user agent? Interested to hear your thoughts. Many thanks, Niels