[exim] debug_print for auth?

Hi,

we can use use debug_print in router to dump some variables, but not with
authenticator, any way to dump variables like $sender_address? following is
a log entry, but no way to know what's really sent to smtp server:

1e6rVz-0002Nr-9b gmail_login authenticator failed H=
gmail-smtp-msa.l.google.com


Thanks,