projects:gpgAuth
The gpgAuth server process is extremely flexible in terms of implementation technologies, with the only requirement being a server-side language with the ability to interface with GnuPG.
I have created examples of server-side implementations for various web-technologies, with the relevant information located within the sub-pages of this section. HOWEVER; these examples are out of date and still use the "emit event" variation of gpgAuth which was only implemented in the gpgAuth client contained in the FireGPG extension for the Firefox browser. I am in the processes of updating the examples to reflect the move to HTTP Header operation. So, yes, the examples here are mostly useless - sorry, I am very busy.
UPDATE: 12/17/2010
I have swapped out the old (now obsolete) PHP example with a server implementation example which targets the current gpgAuth server protocol specification (v1.3.0) - see here: PHP server implementation