This sample is of an OpenID Provider that acts within a controlled set of web sites (perhaps all belonging to the same organization).  It authenticates the user in its own way (Windows Auth, username/password, InfoCard, X.509, anything), and then sends an automatically OpenID assertion to a limited set of whitelisted RPs without prompting the user.

This particular sample uses Windows Authentication so that when the user visits an RP and the RP sends the user to this OP for authentication, the process is completely implicit -- the user never sees the OP.