The ARA extensions are a recent addition to the AAX plugin format, and access to the Avid header files is still on an invitational basis.
Because of that there is no official JUCE support for ARA in AAX plugins yet.
It is possible to make the JUCE integration work with AAX as other forum members have already talked about this, but you’ll have to refer to Avid about the details.
This is another forum thread that you’ll likely find useful