[keycloak-user] Custom Authenticator

Hi folks, I have following use case. There is a service which creates ("registers") a user in keycloak over REST API. After that I would like to login the user automatically. So I need some kind of link which I can return to the browser and which will login the user and redirect them back to some location. Where I have to look? Can somebody give me some advice and some keywords. Thanks for your help Artem