Specifically designed to allow you to authenticate once and then use that as a proof of work across multiple sites, without revealing your identity as being connected across those sites. Here's the math: https://blog.cloudflare.com/privacy-pass-the-math/
I'm not so hot on this stuff so this might be answered or clear on the site and I didn't get it - can the other sites tell who authenticated you? Can the authenticator add metadata?
I'm wondering about other use cases, using it to prove you've paid for something, or donated perhaps. Or passed a daily quiz/challenge. I feel like there's some fun ways of using this.