User can login with "Snap login" repeatedly with the same account

[Victor gonzalez]

Story: on first boot, file ~/.snap/auth.json is empty and once you do "snap login" it shows correctly the username:email information, however users could run snap login repeatedly with the same account(or other accounts).

Environment:
ubuntu-core-16-amd64.img

Products:db,pi3,amd64

Steps to reproduce:

1º Boot core on kvm/qemu
2º Complete console-conf
3º ssh username@localhost
4º Do "snap login <email>"
5º Once you're logged in, do "snap login <email>" again(with the same or any other U1 account)

Current result: user can login twice or more times with the same account or different U1 accounts
Expected result: message tells the user he's already logged in with the U1 account. If any other U1 account is submited, I do not know what's the expected result.
Is it possible to add different U1 accounts? and if so, why they do not appear in ~/.snap/auth.json after you logged in once?