Is there a tool to generate simple CONTRIBUTORS file from a GitHub repository?

I know that there are git commands that could extract and summarize contributors information from a repository such as ones from this link but this is not very useful for a GitHub repository since I'd be getting real names and emails.

I'm looking for a CLI tool with these particular features:

• Find contributors of a local (or remote) git repository.
• Associate those contributors with GitHub usernames.
• Produce an ASCII or Markdown summary.

Is there such a tool? I'm asking because I do not think I am the first one to come up with these requirements. It seems like a simple task.

It's not really a tool but check out the GitHub API: https://developer.github.com/v3/repos/#list-contributors

It does pretty much everything you're asking for, you just need to parse it and produce output. The information is all there. Sample URL: https://api.github.com/repos/glowing-bear/glowing-bear/contributors