@firebase-web-authn/api

A Firebase Extension for authentication with WebAuthn passkeys.

This package contains a Firebase Function that registers and authenticates WebAuthn passkeys, manages public key credentials in Firestore, and cleans up data if the user cancels the process or unlinks a passkey.

Firebase Extension deployment

See @firebase-web-authn/extension for simplified installation using firebase ext:install.

Custom deployment

If you would rather deploy the API from your existing Firebase Functions package,

Set up these services in your project. This must be done both in the Firebase Console and initialized in the application:
- App Check with reCAPTCHA Enterprise or v3
- Authentication with the anonymous provider
- Firestore
- Functions

Run:

% npm install @firebase-web-authn/api --save-dev

Export the API from your Firebase Functions package's main file by calling getFirebaseWebAuthnApi with a config object.

import { initializeApp }                     from "firebase-admin/app";
import { HttpsFunction }                     from "firebase-functions";
import { getFirebaseWebAuthnApi }            from "@firebase-web-authn/api";
import { FunctionRequest, FunctionResponse } from "firebase-web-authn/types";


getApps().length === 0 && initializeApp();

export const firebaseWebAuthnAPI: CallableFunction<FunctionRequest, FunctionResponse> = getFirebaseWebAuthnApi({...});

// Other api...

interface FirebaseWebAuthnConfig {
  authenticatorAttachment?: AuthenticatorAttachment,         // Optional authenticator attachment. "cross-platform" allows security keys. "platform" allows passkey managers. Default behavior allows either attachment.
  authenticatorAttachment2FA?: AuthenticatorAttachment,      // Optional authenticator attachment for second (2FA) factor passkeys. Default behavior follows the main authenticator attachment configuration.
  relyingPartyName: string,                                  // Your app's display name in the passkey popup on some browsers.
  userVerificationRequirement?: UserVerificationRequirement, // Your app's user verification requirement. "preferred" is default.
}

Deploy your Firebase Functions:
```
% firebase deploy --only functions
```

Additional setup

Create a Firestore Database to store public key credentials with the ID ext-firebase-web-authn and location matching the function deployment. It is recommended to choose either nam5 in North America or eur3 in Europe and to enable delete protection:
```
% firebase firestore:databases:create ext-firebase-web-authn --location ${MULTI_REGION_NAME} --delete-protection ENABLED
```

The browser must reach FirebaseWebAuthn from the same domain as your website. Modify your firebase.json to include a rewrite on each app where you'd like to use passkeys:

{
  "hosting": [
    {
      "target": "...",
      "rewrites": [
        {
          "source": "/firebase-web-authn-api",
          "function": "firebaseWebAuthnAPI"
        }
      ]
    }
  ]
}

Grant the Cloud Datastore User and Service Account Token Creator roles to the App Engine default service account principal in Service accounts under App Engine default service account > Permissions.
Grant the Cloud Functions Invoker role to the allUsers principal in Cloud Functions under firebaseWebAuthnAPI > Permissions.