So I need to make a wood gate (between a shed and fence) and I can only attach anything to one of the structures. Is there any sort of hinge or mechanism that will lock itself at 90 degrees(to block access between the two structures) and also allow opening to get access.

Basically just need a gate that is attached to a fence that can stay perpendicular to the fence, but also swing open to allow access when needed. So is there a self locking hinge or some sort of latch that accomplishes this goal?