How to get commits data similar to what's included in the Push webhook

Hi there,

We’re building a little notification system that is supposed to notify developers that their code has been deployed. The push event resulting from a merged PR contains data about all the commits involved in it as well as their authors. Unfortunately, our system is not going to be driven by webhooks but by an event coming from another system. What I will have, to work with, is the commit hash of the PR merge commit.

So, my question is, having only the commit hash, how can I use the v4 (or v3 if much easier) to get the data about commits associated with a merge identified by its commit hash?