Whew this was such a hard and interesting box. I certainly learned a lot! Well- Here come some hints… Bear with me because this is the first time I give out hints.
User1: A certain service on this box will allow you to look into the past, some say that it recorded the forging of the key to open the door!
User2: After a lot of enumeration on User1, you should have found some information that you can use, a certain cat we know may want to play with that - but your journey for User2 does not end here. You will need to be really quick if you want to access what is underneath.
Root: One User can do what the other cannot. When you find a certain file you will realize what it is that you are supposed to do. Tunnel vision is sometimes needed!
PM me if you need any nudges! Thanks @thek for this amazing box!