If we are dealing with a subset of bad cookies, then I suppose it becomes a hard question of what-to-do. We could put something into the code to distinguish and then require a minimum last good date of some sort. It is messy and I wouldn't want to do that, but really I just want to point out that your insistence on it being "impossible" just isn't true. If we just let ourselves revoke everything, then it is much simpler. I wonder how the "known subset of bad cookies" situation arises. I suppose it could, but you could in turn release an announcement telling your users that for all of their protection you are requiring that they login again, insert a minimum required date and move on with life. There are plenty of ways to deal with the situation and none of them are impossible.