How can I scope a user's role to a specific instance of a resource?

[mattcouts]

I have an application that displays information about upcoming events (a birthday party, for example). For any event, a user should be able to serve as either a PARTICIPANT or ADMIN (these are the two application roles) but only for that selected event. They should be able to have a different role in each event.

For example, suppose I am a user. There are three events that I can register for: event#1, event#2, and event#3. I have been asked to serve as an admin for event#2 and I would like to be a participant in event#1. I should be able to fulfill my duties as an admin in event#2 but not in event#1 or event #3. Similarly, I should be able to fulfill my duties as a participant in event#1 but not event#2 or event#3.

How would I scope, for lack of a better term, the user’s role to a specific event so that a user can have different roles in different events?

[mattcouts]

After some further research, it looks like I am looking for Relationship-Based Access Control as opposed to Role Based Access Control.

Here’s an article I read for that information: Understanding a Media Consumer’s Social Graph