Passkeys / WebAuthn

Passwordless WebAuthn sign-in via Firebase Auth passkey integration

Passkeys / WebAuthn

Role

Phish-resistant, passwordless sign-in. The user’s device (Touch ID, Face ID, Windows Hello, Android biometric, hardware key) is the authenticator; the family never holds a password.

Used as a first-class sign-in option on every site’s <AccountPanel> and as the strongly recommended second factor for high-trust actions (subscription cancel, data export, journal unlock).

Free tier

• Unlimited registrations + assertions.
• No per-user / per-event cap on Firebase Spark.
• If we fall back to a self-hosted @simplewebauthn/server flow on the Hono Worker, the only cost is Worker / Firestore quota (already free).

Card / subscription required?

NO. Passkeys are an open W3C standard (WebAuthn level 2 / 3). Firebase’s passkey integration is part of Auth — Spark plan covers it. SimpleWebAuthn is MIT-licensed.

Implementation path

1. Primary path — Firebase Auth’s passkey support. Enable passkeys in Firebase Console → Authentication → Sign-in method. Wire the JS SDK’s passkey APIs into @chirag127/firebase-init so every site’s <AccountPanel> shows a “Sign in with passkey” button.

2. Escape hatch — @simplewebauthn/server on the Hono Worker. If Firebase’s passkey support is incomplete for our needs (e.g. missing conditional UI, missing username-less flow, or an uncovered platform), fall back to a Worker-side WebAuthn flow:

   • /auth/passkey/register/options — issue PublicKeyCredentialCreationOptions.
   • /auth/passkey/register/verify — verify + persist credential ID + public key in Firestore under users/{uid}/passkeys/{id}.
   • /auth/passkey/authenticate/options + .../verify — the authentication side.
   • On success, mint a Firebase custom token via Firebase Admin’s REST endpoint (per firebase-rest-firestore-not-admin.md) and signInWithCustomToken on the client.

   Verify Firebase’s native support before adopting the escape hatch.

Alternatives

• Email link only (loses phish resistance)
• TOTP / SMS as second factor (SMS is paid + phishable)
• Passwords (rejected family-wide — never store or accept passwords)

Swap cost

Medium — credential records persisted under users/{uid}/passkeys/{id} would migrate if we changed the verifier (Firebase native ↔ SimpleWebAuthn). Public-key material is portable; the wire format is the same in both directions.

Why this is our pick

Phish-resistant, hardware-backed, no shared secret. Modern browsers

• OSes ship the UX for free. Passkey adoption is mainstream now (2026), so showing it in the sign-in dialog raises perceived security without any extra dev cost.

Cross-refs

• Firebase Auth provider list
• Firebase Spark
• App Check
• Multi-provider auth decision
• firebase-rest-firestore-not-admin

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