Where can I buy a cat house/kennel which can only be entered by RFID chip?

We feed a stray cat, who probably isn't looking forward to winter, and currently has an injured leg. I will try to get him to the vet.

He occasionally sleeps in the greenhouse - but so do the foxes.

Is there some form of house/kennel that he can sleep in outdoors, but only he can enter, because of his chip (if he doesn't have one, I will have him chipped).