Get list of git commits for a review?

We need to confirm that every commit in our git master branch has been reviewed in some completed CC review.
Most people use the "Add Git Diffs..."  and then do a master-their_branch diff.
After their review is approved and they've merged their branch into master, we'd like to generate a report that shows that every single commit in the master branch has been reviewed.

Any techniques, help or insight on how to start off or to do this will be greatly appreciated.

For example: if there is a Rest API that I can call for each review that lists all of the commit SHAs, then I can write a quick script to call that and then use "git log" against master and thereby confirm that no commit has been left out.

TIA!