The way Kemono did is actually quite simple, if I'm not mistaken, some paid members provide their cookies to Kemono, Kemono uses their cookies to pretend it's the paid member then imports all the stuff on Patreon. The solution is quite simple for Patreon too, they just have to verify the information stored in the cookies, add more verification infos in cookies or some other way you don't know, and use like ip address or even mac address to verify, plus cloudflare, I believe it's hard to get around all these. It's just Patreon is too lazy, there are multiple bugs on their websites never get fixed, for such a simple function website.