prompt or not prompt for password depending on user & client

[powah]

I want the server to prompt or not prompt for the password depending
on the user and client.
How to do that?
Can host based authentication (using ~/.ssh/authorized_keys, etc) do
that?
e.g.
from a known client,
# ssh john@server
prompt for password

# ssh powah@server
no prompt for password

from an unknown client,
# ssh john@server
prompt for password

# ssh powah@server
prompt for password