Authnkey is a credential provider that lets you use FIDO2 security keys (like YubiKey, SoloKey, Nitrokey, or Token2) for passkey authentication on Android.

Many NFC security keys don't work properly on Android. Native CTAP2 over NFC only works with keys that support applet selection using extended encoding, and plenty of keys and smartcards don't. Those keys are stuck with basic U2F tap-to-authenticate, which means no PIN-protected passkeys or discoverable credentials. Authnkey fills this gap by implementing the full CTAP2 protocol.

The app registers as a credential provider, so any app or browser that supports the Android Credential Manager API will offer Authnkey as an option when passkeys are requested.

This also works on devices without Google Play Services, since Authnkey implements the CTAP2 protocol directly rather than relying on Google's FIDO2 API.

Supported features:
- Passkey creation and authentication
- PIN verification
- Discoverable credentials
- Multiple accounts per site
- NFC and USB transports

No root required.
