Aim assist is on by default, in game. There is no option to toggle it on or off.
While some players may welcome aim assist, it presents a notable disadvantage when dealing with strafing enemies, as the AA will slow down your rotation speed as you rotate to catch up with a strafing opponent.
It’s small, but has resulted in many a death. Further options to toggle aim assist, hud, rebind controls on console, etc would all be welcomed with open arms.