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Pornhub Sues Texas Over Age Verification Law
(www.vice.com)
This is a most excellent place for technology news and articles.
The whole point is that the token itself doesn't have any personal info attached to it, only a yes/no and expiry time.
I'll even one up my original suggestion - it uses standard public/private key encryption, where the government issues a simple json token with a yes/no Boolean and a TTL. The public key that can decrypt the tokens is public. Pornhub then decrypts the token and verifies the boolean and expiry date, all without talking to the government at all.