The way to check googlebot (in a way that will be resistant to expansion of Googlebot's IP ranges in the future) is to perform hostname lookup, with dns lookup as well to verify that the rDNS isn't a lie: https://developers.google.com/search/docs/advanced/crawling/...

Indeed, this was one of the things I considered (note I'm not OP), but then I didn't really want to rely on DNS. https://duckduckgo.com/?q=it's+always+DNS

Not a very hard problem; after all, many websites allow full access to Googlebot IP ranges yet show a paywall to everyone else (including competing search engines).

I also happen to ban Google ranges on multiple less-public sites specially since they completely ignore robots.txt and crawl-delay.

Is that how archive.vn works? I've always wondered how they are able to get the full text of paywalled sites like Wall Street Journal who give 0 free articles per month.