>Earlier this month, we announced self-managed OAuth, making it easier for customers to create and manage their own OAuth clients for delegated access to the Cloudflare API.

They're letting you host an OAuth system to approve/deny access to your own resources, so you can build whatever logic you like, rather than waiting on them to allow you to do X under Y conditions. Essentially "log into CloudFlare" -> CF sees you're using this self-managed OAuth -> redirect to your OAuth -> CF trusts your response, and approves access to your account if you approve access.