[exim] Authenticate to relay-host via certificate

Hello,

I would like to use an postfix-mailserver as a relay for my
exim-mailserver at home. The postfix-server authenticates it's users via
x509-certs, so my question is how I can tell exim to use a client-cert
for authentification.
I already had a look at Philip Hazel's exim4-book, but I could find any
hints on that.
Does someone have an idea how to get this working?

Thanks in advance,
Dirk