So, you're looking for some Ruby slippers? (Har! Just teasing, can't resist the chance to toss in a Wizard of Oz...)
Anyway, should be a pretty thin wrapper, perhaps parsing the JSON would be the hardest part. Is this just a GET to read/monitor, or also a POST for write/control?
I find this Ruby on Rails HTTP cheat sheet: http://augustl.com/blog/2010/ruby_net_http_cheat_sheet/
that might be helpful, but a few more questions for you:
Which REST API do you mean? (I'm guessing SNAP PAC vs. groov since you mentioned controllers?) Also hoping you can use http vs. https since that will make things much easier, too?
Note that if you can put your data from the controller into table(s) that might be easier when you get to the parsing part, also a little less overhead on the wire, if that matters.