For Google domains, this is handled by an internal Chrome extension called "cryptotoken". See, e.g. https://chromium.googlesource.com/chromium/src.git/+/master/

For Google domains, this is handled by an internal Chrome extension called "cryptotoken". See, e.g. https://chromium.googlesource.com/chromium/src.git/+/master/chrome/browser/resources/cryptotoken https://chromium.googlesource.com/chromium/src.git/+/master/... For all other domains, there's an open-source, pre-release Chrome extension that handles the site<->token handshakes: https://github.com/google/u2f-ref-code https://github.com/google/u2f-ref-code