side door

noun2

1. •
   A door that is not primarily used as an entrance or exit.

   • Well, I generally come in at least fifteen minutes late, ah, I use the side door - that way Lumbergh can't see me, heh heh - and, uh, after that I just sorta space out for about an hour. — 1999
2. •
   (figurative) A method that bypasses the primary process.

   • The USA won the home-and-home series with the Italians, entering the World Cup through a side door — 2012