Runtime access control by url

Hi,

I'm currently handling access control with "AuthBasicProvider ldap dbd".
I'd like to get rid of the growing list of <Location> directives in
our httpd.conf and lookup each request url against a database, to
check whether it requires a login.
Visitors should be able to browse the website without an account, and
only be asked for one for specific URLs.

I've tried using a PerlInitHandler in <Location />, but am unable to
get it to work.

It seems that the Auth/Authz phases are only run when the <Location />
contains a "Require" directive.
It appears that Apache2::Access->requires() is only a getter, so I
can't switch "Require" on within my PerlInitHandler.
But if I set "Require" in httpd.conf, I can't unset it for URLs that
shouldn't require a login.

Am I going about this the wrong way - and has this been solved before?
Cheers,
Carl