We've recently moved some of the REST API documentation. If you can't find what you're looking for, you might try the new Branches, Collaborators, Commits, Deploy Keys, Deployments, GitHub Pages, Releases, Metrics, Webhooks REST API pages.
コラボレータ
Collaborators APIを使うと、リポジトリでコラボレータの追加、招待、削除が行えます。