Login or unlock screen on a Mac using an NFC tag?
In earlier versions of OS X (i.e. 10.9 and older) you had the /usr/sbin/pcscd executable, which the driver that comes with your ACR122T dongle can talk to.

In the latest OS X (10.10), pcscd has been replaced by something new called com.apple.ctkpcscd, which will be running in a default install of Yosemite.

The documentation for this new daemon is available from:

https://smartcardservices.macosforge.org

Here you can also get the source code, etc.