Do you have any articles to learn more about this? I’ve been thinking about this exact problem with many companies requiring hoops like phone numbers for antispam purposes. But all they really care about is that it’s a human not a bot.

So some way to have an independent central website with list of valid but anonymous keys could be used to sign up for any online service and prove you’re a human. Sort of like id.me . I’d almost be okay needing to get a letter in the mail for initial registration.