What Are Passkeys? A Developer's Guide to WebAuthn and FIDO2

Passkeys replace passwords’ shared-secret model with public-key cryptography: a device stores a nonextractable private key in secure hardware while the server retains only its matching public key. Built on WebAuthn, the browser API, and FIDO2, which also includes the protocol for communicating with authenticators, passkeys authenticate users by signing fresh server-issued challenges rather than transmitting reusable credentials. Their origin binding prevents credentials registered for one domain from being used on phishing sites, while one-time challenge signatures cannot be replayed if intercepted. Synced passkeys improve usability and device recovery by storing encrypted credentials in cloud keychains, whereas device-bound passkeys on hardware security keys provide stronger physical assurance but require separate recovery planning. The technology is now natively supported across major platforms, and the text positions it as a practical authentication option for developers, while noting that secure recovery methods and protection of synced-keychain accounts remain important considerations.

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