ACLs via external hooks

Hi,

inside a larger project with quite dynamics access rights (yes, true)
I would like to check the access rights (and logins?) against external
sources.

Eg., just like a "pre-commit" - hook but for reading, too. Or may I
insert something into the configuration which will do that?

And yes - the documented dir-based ACLs will not work 'cause its too
much. External source means, I may ask a server has_rights(user,path)
and will return yes/no or exit 0/exit 1 or similar. For pre-commit it
would work.

Is this possible?

CU

Rajko