FIDO Bridge for Android - User Manual

Overview

Modern Android devices do not fully support FIDO2 over NFC, meaning they cannot perform certain operations, like PIN verification and discoverable passkeys, with NFC security keys out of the box. This limits the ability to use hardware security keys for passwordless authentication on many Android devices.

FIDO Bridge is Token2’s repackaged version of the open-source Authnkey Android credential provider. It brings improved CTAP2 support for NFC keys on Android by acting as a credential provider, enabling better communication with FIDO2 keys over NFC.

The upstream Authnkey project solves the Android NFC FIDO2 limitation by bridging CTAP2-style capabilities. It is distributed as an APK on F-Droid and now also available on Google Play under a new app ID and name. The repackaged app also includes a link to Token2’s companion app for advanced key management.

1. Installation

From Google Play

• Open the Google Play Store on your Android device.
• Search for FIDO Bridge
• Install the app.

This version has a unique package ID and new branding so it can coexist with Authnkey package.

From F-Droid

• Visit F-Droid and search for Authnkey.
• Download the APK.
• If needed, enable installation from unknown sources in Android settings.
• Install the APK manually.

Authnkey is exactly the same underlying project — no functional changes except distribution details.

2. Initial Setup

• Open FIDO Bridge.
• The app will register itself as a Credential Provider / Passkey provider on your device.
• Go to System Settings → Passwords & accounts → Passwords, passkeys, and autofill. (exact location and setting name may vary)
• Enable FIDO Bridge (or Authnkey) as your credential provider.

This tells Android to present FIDO Bridge as an option when a site or app requests passkey or security key login.

3. Using with Security Keys (USB & NFC)

Supported transports:

• USB-C (plug-in directly or via USB-OTG adapter) - This transport is also supported by the native Android credential provider.
• NFC (tap your NFC key against your phone) - Using NFC with PIN-protected credentials is not natively supported; FIDO Bridge/AuthnKey is currently the only available solution.

FIDO Bridge/AuthnKey  enables PIN verification, discoverable passkeys, and full CTAP2 workflows with security keys.

Authenticating (Login Flow)

• On a login screen that supports passkeys or FIDO2 login, choose FIDO Bridge (or Authnkey) as the credential provider.
• Use your hardware key:
  • USB: connect your key via USB-C/OTG
  • NFC: tap your key to the phone NFC area
• Enter your key PIN if prompted.
• Touch the key to confirm.

FIDO Bridge handles communication so that features Android doesn’t natively support (especially NFC CTAP2) are usable.

4. Token2 Companion App (Optional)

Inside FIDO Bridge, there may be a link to Token2’s Companion App — a management app for advanced key features such as TOTP profiles, passkey lists, and advanced FIDO2 configuration settings. The companion app provides a richer interface for key management and is optional. However, for basic FIDO2 management, AuthnKey/FIDO Bridge offers sufficient functionality for regular users.

Tap the link inside FIDO Bridge to install the Token2 Companion App from Google Play or another source.

5. Tips, Notes & Best Practices

• Android’s native support for FIDO2 NFC is still limited; FIDO Bridge exists to bridge these limitations.
• Some apps and browsers let you select which passkey/credential provider to use at login. If the system doesn’t prompt automatically, open the passkey dialog and choose FIDO Bridge.
• Use a PIN on your hardware key for stronger security.
• Keep Android up to date.
• Install browser versions that support FIDO2/Passkeys natively, such as Chrome.
  
  

Frequently Asked Questions

Do I need Google Play Services for FIDO Bridge?
No — installing from Google Play simplifies updates and permissions but is not required.

Does this project differ from the original Authnkey?
No — the repackaged app only modifies the branding and package ID to support distribution via Google Play. The underlying AuthnKey project remains unchanged. All modifications are documented in the compilation assistant Python script, which is published in this GitHub repository.

Does FIDO Bridge work with all FIDO2 keys?
It works with CTAP2-compatible keys and cards; USB and NFC should work. Actual behavior depends on the device and key capabilities.

Summary