An Authenticator s a cryptographic entity used generate a public key credential and registered by a Relying Party (i.e. an application). This public key is used to authenticate by potentially verifying a user in the form of an authentication assertion and other data.
Authenticators may have additional features such as PIN code or biometric sensors (fingerprint, facial recognition…) that offer user verification.
The authenticator may have different forms. The most common form is a USB device the user plugs into its computer. It can be a paired Bluetooth device or a card with NFC capabilities.
The authenticator can also be software based and integrated in an Operating System ; for example the smartphone using Android or a laptop with Windows 10 can act as an authenticator.
