Can someone tell me where to get the code to the cellar in the abandoned compound?

[Maenethal]

Searched the whole map and killed a bunch of zombies hoping one might drop the code, but no luck. Gave up and moved on before I took too much infection.

[Radish]

Coded cellar doors are a perk you get in the knowledge tree, kind of like the bolt cutters, the codes are used to go inside some areas.