There is no registering or certifying a Service Dog in order to gain public access.
I'd recommend reading the ADA laws regarding service animals.
Revised ADA Requirements: Service Animals
ESA do not have public access rights, but medical alert dogs do.
Please Don't Pet Me
The ADI offers testing, although like I mentioned there isn't any official testing. But I'd recommend training your boy to the point where you're confident he could pass this. If you really want to have something on paper, you could do what I did. I contacted a local certified dog trainer (certified in general dog training, not service dogs) and sent him the link to this test. I asked him if he would accompany us out and about, test us, and do a write up on what he saw/observed. I also demonstrated a few of my boy's SD tasks, although it sounds like you wouldn't be able to unless you have an attack during the test.(Due to this, it really is just a write up on the dog's stability and training in public)
Assistance Dogs International : Public Access Test