yubikey-agent is a seamless SSH agent specifically built for secure hardware tokens such as YubiKey (and other PIV tokens). It aims to replace the standard SSH agent with a version tailored for these security devices; the key is generated on the hardware token (so it can’t be extracted), every session requires a PIN and a physical touch, and the agent is resilient to unplugging, sleep/suspend, and restarts. Setup is simple, one command and one environment variable, and then the agent just runs in the background. ...