Web Authentication (WebAuthn) is a web standard published by the World Wide Web Consortium (W3C). WebAuthn is a core component of the FIDO2 Project under the guidance of the FIDO Alliance. The goal of the project is to standardize an interface for authenticating users to web-based applications and services using public-key cryptography.
Similar to legacy U2F, Web Authentication is resilient to verifier impersonation, that is, it is resistant to active man-in-the-middle-attacks, but unlike U2F, WebAuthn does not require a traditional password. Moreover, a roaming hardware authenticator is resistant to malware since the private key material is at no time accessible to software running on the host machine.
FIDO2 vs U2F
FIDO2 is the successor of the FIDO Universal 2nd Factor U2F legacy protocol. FIDO2 authentication has all the advantages of U2F—the primary difference is that a FIDO2 authenticator can also be a single-factor (passwordless) authenticator. The U2F protocol is designed to act as a second factor to strengthen existing username/password-based login flows.
Authentication for websites
WebAuthn/FIDO2 is supported by major sites like Google, Facebook, Twitter, or GitHub. See https://www.dongleauth.com/ to find other websites and links to setup documentation.
Modern browsers like Firefox and Chromium support WebAuthn authentication standalone, additional dependencies are not required.
For a demo site to test the WebAuthn authentication process, see https://webauthn.io/.
Local Linux authentication (PAM)
For using U2F authentication see U2F.
Using a FIDO2 authenticator for local login
The FIDO2 specification includes an extension called HMAC Secret Extension (hmac-secret), which allows the secure use of a shared secret stored on the authenticator for local authentication.