Like this is a security problem, straight up. I would hope that you can agree on this and that not securing your API is bad.
I only got a few posts into the thread before Twitter booted me out for not having an account, so maybe there's some context I'm missing, but what kind of "not securing your API" are you talking about? The fact that a thir party, explicitly authorized the the user, was able to make actions on the user's behalf, doesn't make it secure, it makes it functional.
Earth: https://en.wikipedia.org/wiki/Facebook%E2%80%93Cambridge_Ana...
FB gave them data about friends, when it was supposed to only give them data about respondents. Totally different situation.
If I approve an access request for a low level engineer to get a single repo from github, and github lets them access every repo on our orgs account, that's a huge fuckup by github, not me.