Wiktionary
on a need-to-know basis
adv. (context of the giving of information English) remaining secret or hidden until it is needed to be known (by a particular party).
Usage examples of "on a need-to-know basis".
Therefore, Gubbeen and the others were on a need-to-know basis only, as far as the specific details of our upcoming attack were concerned.
First and foremost, information here is handed out on a need-to-know basis and, quite frankly, she has not needed to know.
There were some special sections that I could not, on a need-to-know basis, involve myself with.
From what he'd already seen, the Connection ran his organization on a need-to-know basis, and the driver didn't need to know anything about the stranger braced in the open doorway as he got the van up to speed.