Ask HN: How to review GitHub PR with multiple authors?

Github's pull request and commenting on code commits and pull requests is amazing. But when reviewing pull requests where multiple persons have contributed code to the same PR, it becomes quite complicated to map code in PR to the commit or the original author.

Say A did a commit `aaa` and B did a commit `bbb`, and there is a pull request with these 2 commits, and I comment on the pull/1/files, it doesn't link to either `aaa` or `bbb` nor its original authors. Is there anyway to do this without manually finding each of the author informing each of the author that your code requires improvement.

I'm trying to do something like git-blame on PRs or link line numbers to commit hashes. Github doesn't support this feature. Is there any workaround to do this, or if not for PR, is there anything else that I can use to do this ?