Test fitting the leg to apron bridle joints. The fit has to be just right because all three legs (and the assembled stretchers) will be slid onto the apron at the same time.
Precise and Accurate Layout: The First Step in Cutting Joinery By Hand
Here I've laid out and roughed out a joint in the apron, which will accept a leg. The joint is a bridle joint with sliding dovetail. It's all hand work from here.