Great idea, but personally I've discarded UML for years. And there are plenty of posts in the Google result to describe OAuth2 flow. My post is not intended to describe the OAuth 2 concept, and but for practice(and for a none English person, describe a concept clearly in English is a little diffcult).
Written by Hantsy
Self-employed technical consultant, solution architect and full-stack developer, open source contributor, freelancer and remote worker