Some more info on OAuth 2.1 from the @oktadev blog:
OAuth 2.1: How many RFCs does it take to change a light bulb?
https://developer.okta.com/blog/2019/12/13/oauth-2-1-how-many-rfcs
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aaronpk_tv
How are the new OAuth2 things going to impact IndieAuth if at all?