As Bertrand Fan puts it in his project writeup, “If you work in tech, you probably have a YubiKey,” and he personally uses a YubiKey5C Nano. These little devices plug into your computer and provide a convenient way to produce two-factor authentication when pressed. The only "problem" is that you have to touch it with your finger to activate the authentication. Normally this is actually pretty easy, but when your computer is attached to a dock, reaching this capacitive switch is inconvenient, and using a USB-C extension cable can be difficult to tap consistently.
So what is one to do in this situation? If you're Fan, it's to build an auxiliary finger of course! His new solution uses a 3D-printed digit connected to a 28BYJ-48 linear actuator assembly to activate the switch on command, controlled by an ESP8266 board. The device is actuated over WiFi, using a macOS keyboard customizer called Karabiner-Elements, and a bit of scripting to enable triggering via the keyboard.
With a bit of fiddling with the grounding setup to allow the finger to emulate a human’s capacitance, it can now tap the YubiKey without Fan having to move his hand from the keyboard. While one could argue that he’s pressing a button... to press another button, he’s now able to hit the particular button that he wants, without having to reach unnecessarily!