If a site (or the WAF in front of it) knows what it's doing then you'll never be able to pass as Googlebot, period, because the canonical verification method is a DNS lookup dance which can only succeed if the request came from one of Googlebots dedicated IP addresses. Bingbot is the same.
That's maybe a bit insane to automate at the scale of archive.today, but I figure they do something along the lines of this. It's a perfect imitation of Googlebot because it is literally Googlebot.
Presumably they are just matching on *Google* and calling it a day.
Which specific site with a paywall?
Why? in the world of web scrapping this is pretty common.
Maybe they use accounts for some special sites. But there is definetly some automated generic magic happening that manages to bypass paywalls of news outlets. Probably something Googlebot related, because those websites usually give Google their news pages without a paywall, probably for SEO reasons.
The curious part is that they allow web scraping arbitrary pages on demand. So if a publisher could put in a lot of arbitrary requests to archive their own pages and see them all coming from a single account or small subset of accounts.
I hope they haven't been stealing cookies from actual users through a botnet or something.
It would be challenging to do with text, but is certainly doable with images - and articles contain those.
For those that don't , I would guess archive.today is using malware to piggyback off of subscriptions.