I took a look at it. iTunesSpy seems to be a companion to the iTunesWatcher program. iTunesWatcher sits in the taskbar and watches the tracks you play in iTunes, then notifies your blog about them when they change. iTunesWatcher is part of your blog and receives these notifications.
The “authorization key” is like a password. You can set it to whatever, but it must be the same between your iTunesWatcher and iTunesSpy. This protects your blog from having somebody else insert their own tracks into it. See?
This is similar to other “now playing” type of blog plugins. I personally use CG-WhatTunes to do this same thing, along with a program called “iTunesBlogger” to sit in the taskbar and watch iTunes change tracks. I also have plugins for Winamp/Windows Media Player/musikCube which can talk to CG-WhatTunes, so that it’ll work no matter what player I use.