Still a n00b here, so ballsy of me to toss out this mention of something off-property (but “neato burrito”) that I recently discovered:
Ever checked out PIPEDREAM.COM? Looks very promising for round-tripping GET calls, variable storage, OAuth flows, etc. which might fill the gap for users with multiple (esp. not linked or co-located) controllers.
It’s rather like the love child of IFTTT, Webhooks, Postman, APIlio, Heroku, TheThings, Yonomi, Yahoo Pipes! (RIP), and Stringify minus any particular focus on HA. And easier/faster/tidier to set up than most of those other services. They offer (generous) free and reasonably-priced paid tiers.
Has definitely saved my bacon when trying to troubleshoot some HTTP request bugaboos, by allowing me to specify custom responses to GET or POST inputs.