[keycloak-user] Multiple user stores / Domain separation

Hi all, In case multiple user stores are connected (e.g. different Active Directories). Is there any build-in option to provide some kind of domain discriminator (e.g. drop down menu) on the login page? If not, are there any proposals or best practices howto achieve this? How does Keycloak handle the issue that a the username is not unique in case of multiple userstores? Thank you, Regards, Thomas