back door — ONAD

back door /ˈˌbak ˈdô(ə)r, ˈˌbæk ˈdɔ(ə)r

▸ noun the door or entrance at the back of a building.

▪ a feature or defect of a computer system that allows surreptitious unauthorized access to data.

▸ adjective (also backdoor) [attributive] (of an activity) clandestine; underhanded:

backdoor private deals.

– PHRASES
through the back door (also by the back door)
using indirect or dishonest means to achieve an objective:

this form of franchising will be seen as privatization through the back door.