This is a 3D printed adapter that should fit into any hot shoe flash socket. I made it to access the flash trigger signal and use it to confirm that the camera took a photo.

The adapter uses two pogo pins as contacts for the ground tab and the center trigger output. I used a 2.5mm Jack socket as the external connector. There is also a top mount tab with 2x M3 holes to attach something on top of the adapter.

The trigger signal requires external pullup resistor (eg. 10k) to 3.3v. Haven't tried higher voltage.