Scoop would have to create an account for somebody logging in via OpenID and have some sort of system to determine internally whether they're password or OpenID authenticated. A simple flag in the database would probably do it.
So from the user's point of view, they create an account either the normal way or by selecting a username and providing their OpenID URL; account creation is done either the normal way or by verifying identity using OpenID. The user would then have the option of logging in using a password (if they created an account the normal way) or via OpenID (if they created an account that way).
Internally, you'd have verification either via email or OpenID, and login either via password or OpenID; either way there's an account in the Scoop db and a site cookie on the user's computer once they're logged in.
Being Scoop, there would of course be a Site Control to turn the OpenID login system on and off :-)
On the server end, /user/nick/openid could contain the OpenID auth info, generated by their library. A var to turn on the OpenID server system of course, and probably a user pref for the user to choose if they want to use that OpenID identity URL or not.
It doesn't sound like it would be too hard, provided the perl module you link to are reasonable to work with.
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