I've coded in C# to report to PSKReporter. The interface is interesting. One definitely needs to reference the SDK as it's not a simple RESTful POST. One thing of note is that VaraC reports its mode, at least from what I see in the ADIF log, as VARA. That's absolutely fitting and proper; however, the VARA mode is neither supported by the ADIF 3.1.2 specification nor PSKReporter. I'm not sure what would be involved to get VARA registered as a bone fide mode, but it looks like that would need to occur to get things reported properly on PSKReporter.

For logging, sending a UDF packet with an ADIF record should be sufficient. N1MM+ uses a proprietary format, but that could be a possibility too. However, ADIF would be the better and more compatible option. Another option is to send UDP broadcast packets in the same format as WSJT-X. There are several code examples for various languages on GitHub. Creating and sending the WSJT-X Status and Heartbeat packets would immediately make VaraC compatible with GridTracker and other apps that already work with WSJT-X. If you would like to discuss further and to go into the packets or see an example, drop me a line. I've done the work to receive and decode these packets for my own logging program. While you'd be doing the encoding, it's a similar principle.