Lots of people are asking why Anthropic and OpenAI don't support OAuth, so you can bounce them through those providers to get a token that uses their API budget for your app
My guess: they're worried malicious app developers would use it to trick people and obtain valid API keys
Imagine a version of my dumb little "write a haiku about a photo you take" page which used OAuth, harvested API keys and then racked up hundreds of dollar bills against everyone who tried it out running illicit election interference campaigns or whatever
https://tools.simonwillison.net/haiku