MacOS Yubikey Smartcard/PIV instructions.

Installation instructions for MacOS using "brew" and Yubikey tools. This document instructs users on setting up their Yubikeys (PIN, etc.) and uploading the public key to Key9.

The advantages of PIV (Personal Identity Verification):

1. Works with older Yubikeys.

2. Can work across multiple operating systems (Windows, Linux, MacOS)

3. The SSH private key is stored directly on the Yubikey itself.

4. It's possible to pass PIV data to other SSH sessions via forwarding.

The disadvantages of PIV:

1. More steps to get set up.

2. To use other operating systems, SSH must be configured to use Yubikey PIV.