There is a new PHP4 extension being developed for use with PHP 4.0.3pl1, Apache 1.3.14 and Linux Kernel 2.2.10 that allows a client-server type relationship for the exchange of sensitive data between applications. Taken from the Scripthash website:

During module initialisation a shared memory segment is created and initialised with a randomly generated secret. This segment remains attached across the subsequent forks which create the Apache children and thus the children have access to the secret. The module implements a single function scripthash() which when called returns an MD5 hash of the secret and various attributes of the call. This hash can be used by external programs (scripthash "clients") to securely return privileged information to the caller.

A very interesting project, indeed.