Apache::ssllookup is a glue layer between perl handlers and the mod_ssl public api. under normal circumstances, you would use $r->subprocess_env() to glean information about mod_ssl. for example,

$request_is_over_ssl = $r->subprocess_env('https');

however, this is only possible after mod_ssl runs its fixups - that is, perl handlers can only accurately check the subprocess_env table for mod_ssl information in the perlresponsephase or later.

this module allows you to query mod_ssl directly via its public c api at any point in the request cycle. but without using c, of course.