An intelligent coworker friend of mine brought up a question to me that I was uncertain how to answer and I'd like to pose it to the world.

If a RESTful endpoint uses token-based authentication, aka a time-based token is required to access a resource and that token expires after a certain amount of time, would this violate the RESTful principle? In other words, if the same URL expires after a certain amount of time, so the resource returns a different response depending when it was requested, is that breaking REST?