It's impossible to provide details about the OAuth2 beta testing protocol. I have searched the official website and blog, but nothing was written or announced about it. There are a few projects hosted on various open source platforms that have OAuth2 protocol added as a sideload for WeChat. You can browse them using the results from Google Search. Access the page and visit the GitHUB project as a starting point.
Google Search results: https://goo.gl/8hsgIl