doesn't need full fledged activitypub, just a common place to login might just do it federated way of "here is my domain, here is DNS entry pointing to my iden

doesn't need full fledged activitypub, just a common place to login might just do it federated way of "here is my domain, here is DNS entry pointing to my identity server to talk with", that way it isn't even tied to single identity service, but a given user will need to use only single login for all of the servers.