[Dovecot] Authentication a la Postfix's Mynetworks

[Asai]

 Is it possible to automatically authenticate Dovecot users using the 
same type of mechanism which makes Postfix able to simply check SMTP 
users using the  mynetworks variable?

Basically I would like to be able to authenticate users on my designated 
networks automatically, and require a password for those outside this 
network.

Is this possible?

--
--asai