Where would I go to get a good pen test done on a PaaS service (specifically, LittleHorse Cloud, which is not a normal webpage app with a login: https://littlehorse.io )

We used https://www.cobalt.io/ though I also don't have a lot of references in the space. Reasonable, fast, good communication, good findings (the first year/pass especially). Had no urge to look elsewhere afterwards.

Awesome, thanks!