a polkit agent in 145 lines of code, because polkit is dumb and none of the other agents worked
polkit is dumb, and never works.
so here is probably the simplest version you can have (except the first one that just ACKed every call), 97 lines of C++ and 45 lines of C, in total 142 lines of code.
it just uses kdesu to call a helper as root to send the reply, so all requests requires the user to enter the root password.
Write a simple replacement for polkit itself, it's a simple dbus API and 90% of what it provides is never used.