AFAIK there's no "certifying body" that would be able to provide an external "certification".
In any case Filip Skokan has essentially made a career out of building open source OAuth stuff, so even if it's a bit humorous that he certifies his own stuff, it's likely that this implementation is one of the most compliant out there.
In any case Filip Skokan has essentially made a career out of building open source OAuth stuff, so even if it's a bit humorous that he certifies his own stuff, it's likely that this implementation is one of the most compliant out there.