[Exim] Authenticating against user account

How do you set exim to authenticate against the user's unix login and
password? I'm using Debian and basically want to have each user with an
account on the machine using the same login and password as their shell
login.

Secondly I'd also like to force TLS and a secure method of authentication to
be used. How do you do this? Thanks,

David

P.S. Please CC your response to me. Thanks