That's impossible. If you're trying to stop automated scraping of your data, then limit the access rate per IP. That won't really help things since someone can

That's impossible. If you're trying to stop automated scraping of your data, then limit the access rate per IP. That won't really help things since someone can just tell the script to slow down to the pace of a normal user. If a user can access unauthenticated data, so can a computer.