FIDO U2F

Full Title or Meme

A family of standards^[1] for adding more factors to an existing interchange.

This spec is partially succeeded by Web Authentication.

Existing Authentication protocols based on a User Name and Password are insufficient in a world were so many Users depend on the internet for so much of their daily lives. The first attempt at Multi-factor Authentication was Smart Cards using X.509 Certificates. This scheme worked for large Enterprises but was never accepted by regular Consumers of the internet.

All solutions depend on Late Binding Tokens that "account at a particular origin (of the Relying Party, such as http://www.company.com) the device creates a new key pair usable only at that origin and gives the origin the public key to associate with the account."
Universal Serial Bus (USB) tokens are now widely available, most allow late binding of the user to the Web Site that requires this factor of Authentication.
Other networks, link NFC or Bluetooth are offered for small hand-held devices, but have not been as successful as the USB versions.
Initially the U2F functionality is available through JavaScript programs in the browser.
The spec claims that the same functionality could be embedded in Native Apps in the browser, but does not explain how this might be trustworty.

"Why Johnny Doesn’t Use Two Factor: A Two-Phase Usability Study of the FIDO U2F Security Key" https://fc18.ifca.ai/preproceedings/111.pdf

Angelo Liao +1, Introducing Web Authentication in Microsoft Edge. (2018-07-30) Microsoft https://blogs.windows.com/msedgedev/2018/07/30/introducing-web-authentication-microsoft-edge/
Also see the page FIDO UAF for the Universal Authentication description.