Patio Light Fixture To Electrical Socket

Question

So we are putting up some string lights on our covered patio and want to use those instead of our patio light fixture right outside the door. I've removed the light fixture and there is an octagonal electric box. I was hoping to put an electrical socket in there and plug the string lights in through there to control with the light switch inside the house. What can I use the fit over that octagonal box and keep the socket in use and weather proof? I'm having the hardest time finding something to work. The octagonal metal box is in brick and mortar. I'd prefer to NOT remove the box and replace with a different one if possible. The box looks like this:

Answer 1

One possible idea for this connection is to look for an octagon electrical box cover that looks like this:

Then acquire a box to box electrical connector that looks like this:

This can then be joined to a back hole in an appropriate electrical box that gets surface mounted to the face of the wall. This box would then accommodate the needed outlet and exterior in-use cover assembly.