If you're looking for open source WebFinger client and server software, visit this page:
https://www.packetizer.com/webfinger/software.html
Packetizer's server has been updated now that RFC 7033 has been published to support only the functionality specified in the RFC. Whereas version 1.2 supported RFC 6415, that functionality has been removed. This made the code much simpler and easier to follow. (Tip-of-the-hat to all the IETF folks who beat me up over trying to hold on the the legacy XML syntax. You're entirely correct that JSON was the right way to go.)