Why smartphone as a security key?
Carrying and using hardware keys is cumbersome and unnatural for users, whereas Smartphones are universal, ubiquitous, natural, and most importantly rarely out of touch with users.
Modern smartphones utilize trusted biometric authentication mechanisms for unlocking the device that is available for resident apps. They cannot, however, extend this trust through modern FIDO2 standards beyond the phone.
IDmelon has accomplished this through advanced BLE mechanisms enabling the phone to be a certified FIDO2 Security Key.
A simple tap of an authenticated smartphone is all that is needed to complete passwordless authentication everywhere FIDO2 is supported.