!!! Overview
[{$pagename}] is an [Authenticator], specifically, a [FIDO Authenticator] that supports the [Universal Second Factor] [FIDO protocol][{$pagename}], technically, is only supported for [Multi-Factor Authentication] ([MFA]) and not [Passwordless Authentication] as in [CTAP2] and [WebAuthN]

!! [{$pagename}] interface types
At the moment (2017-04-02) three interface types are specified in [FIDO] [U2F]. 
* [Universal Serial Bus] ([USB])
* [Near Field Communication] ([NFC]) 
* [Bluetooth] (Classic and Smart aka Low Energy ([BLE])). 
Unlocking is a test of [user] physical [presence] and requires a token-specific [Authorization Gesture], such as pushing a button on a [USB] device, tapping a [U2F] device to an [NFC]-enabled device such as a mobile phone or tablet, or pressing a button on a [BLE]-enabled token or fob. 

The user can use the same FIDO [{$pagename}] on all online services that support the [{$pagename}] [protocol].!! [{$pagename}] and [WebAuthn Authenticator]
Existing [FIDO] [U2F] Security Keys are largely compatible with the [Web Authentication API] standard, though [Web Authentication API] added the ability to reference a unique per-account "user handle" identifier, which older hardware tokens are unable to store.
[Authenticators] that only support the §8.6 [FIDO] [U2F] Attestation Statement Format __have no mechanism__ to store a user handle, so the returned userHandle will always be null.!! More Information
There might be more information for this subject on one of the following:
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