@arteteco OAUTH already makes that possible. Just need the activity pub services to start supporting it (some do, not many)
Oauth can work even between different servers? I used it once but the programs were on the same machine
@arteteco depends what you mean. It means that you can sign on with one click on any server which uses the OAuth provider you are registered with.
Usually when you see things like "sign on with your facebook account" that is OAuth