The Optimus Keyboard uses mini OLED displays on each key in order to dynamically customize the layout and function of a keyboard suitable to the application at hand.
Makes me think of something like the following for identity transactions, with some typical identity operations thrown in (with a little but not much thought to logical organization). The purple keys are meant to represent operations performed at the user's Identity Provider. The greeen, yellow, and red keys for responding to identity requests (with some representative answers). Other "non-identity" keys are greyed out, reproducing the visual effect of the similar Cardspace behaviour.
When not warranted by some request for identity, the keys would show whatever other letter/function/operation was appropriate.