Configuring a Radius server on the ASA can be done be similar to this:
http://www.cisco.com/c/en/us/support/docs/security/asa-5500-x-series-next-generation-firewalls/117641-config-asa-00.html
I have not used AuthAnvil two factor authentication personally, but have implemented Duo passcode with Cisco ASA. This has worked very well so far. There are a few ways to go about this (Radius proxy or LDAPs), and the easiest method I have seen is to use Duo with LDAPs. An example of this is here:
https://duo.com/docs/cisco