Webplayer Facebook game- is a PHP script and a Unity script sufficient?

Or is a some kind of plugin required?

For my first game, a single-player iOS only game, I had some limited Facebook features ( post screenshots and high scores ) that I achieved using the Prime31 Social plugin. My next one is a 2-player game that I want to be a fully integrated Facebook game. Basically I intend for it to do everything that Words With Friends does. ( Including getting 5 million players of course... hahahaha! )

I already RTFM over at developers.facebook.com; but it seems to be assuming that a web-based game is running directly as part of the webpage, not as compiled code in an embedded Unity player.

Before I dig myself into too deep of a hole, can I use Unity's WWWForm and WWW in a single script, talking to a PHP file on my server, to do everything Facebook needs me to do? And if not, what else is it going to take? I couldn't figure out from Facebook's technical guide how I would actually start a 2-player networked game once a friend has been sent a challenge through Facebook and accepted it.