webauthx

Imported from wevm/webauthx (SKILL.md). Install upstream with npx skills add wevm/webauthx. Copyright stays with the author.

webauthx

Set up production-ready WebAuthn passkey ceremony orchestration using webauthx.

Read README.md for the full API reference. Read examples/hono/ for a simplified reference implementation. The example prioritizes clarity over production hardening, so follow this checklist for production.

Setup

Install webauthx and import from webauthx/server and webauthx/client.

Registration Flow (Sign Up)

1. Server: call Registration.getOptions({ name, rp }). Returns { challenge, options }.
2. Store the challenge server-side (signed cookie, DB, or KV). Must be single-use and short-lived (≤5 min).
3. Client: pass options to Registration.create({ options }). Triggers the browser passkey prompt. Must be called from a user gesture (click/tap).
4. Client: POST the returned credential to the server.
5. Server: consume the stored challenge, then call Registration.verify(credential, { challenge, origin, rpId }).
6. Persist result.credential.id and result.credential.publicKey associated with the user.

Authentication Flow (Log In)

1. Server: call Authentication.getOptions({ credentialId, rpId }). Returns { challenge, options }.
2. Store the challenge. Same rules as registration: single-use, short-lived, server-side.
3. Client: pass options to Authentication.sign({ options }). Must be user-initiated.
4. Client: POST the returned response to the server.
5. Server: consume the stored challenge, look up the stored publicKey by response.id, then call Authentication.verify(response, { challenge, publicKey, origin, rpId }).
6. On success, mint a new session (rotate any existing session ID).

Best Practices

Endpoints

• Keep challenge generation and verification as separate routes (e.g. POST /register/options + POST /register/verify). Don't combine them into a single endpoint.

Cookies

• Use separate cookies for challenges and sessions with different names and TTLs. Challenge cookies are short-lived (≤5 min) and consumed on verify. Session cookies are long-lived and persist across requests.
• Always set HttpOnly, Secure, SameSite: 'Lax', and Path: '/' on both. Use signed cookies to prevent tampering.
• Don't store user data in the session cookie. Store a session ID or credential ID, and look up the rest server-side. Keeps cookies small and avoids stale data.

Auth Middleware

• Protect authenticated routes with middleware that reads the session cookie, looks up the credential/user, and returns 401 if invalid.
• Keep it generic: check session, load user context, call next. Don't put business logic in the middleware.
• See examples/hono/ for a reference pattern.

UX

• Registration.create and Authentication.sign must be called from a click/tap handler. Browsers reject unprompted WebAuthn calls.
• Handle cancellation gracefully. Users can dismiss the passkey prompt at any time. Catch the error and let them retry without reloading the page.
• Let users register multiple passkeys so they aren't locked out if they lose a device.
• Show a passkey management UI where users can see their registered credentials (credentialId, createdAt, lastUsedAt) and remove ones they don't recognize.

rpId

• Keep rp.id stable. Changing your rpId invalidates all existing credentials. Pick it once.

Security Checklist

Follow every item below for production deployments.

Transport

• WebAuthn only works over HTTPS (localhost is the only exception).
• Set Strict-Transport-Security with includeSubDomains and preload.
• Set Cache-Control: no-store on all ceremony endpoints.

Origin & rpId

• Hardcode origin and rpId on the server. Never accept them from the client or derive from request headers.
• rpId is a registrable domain (e.g. example.com), no scheme, no path. To share passkeys across subdomains, use the parent domain.
• origin must exactly match what the browser sends (e.g. https://app.example.com). For multiple origins, use a strict allowlist.

Challenge Lifecycle

• Challenges are single-use. Consume (delete) the challenge on the first verification attempt, whether it succeeds or fails.
• Expire challenges after 1-5 minutes (the Hono example uses 300s).
• Store challenges server-side in a signed cookie, database, or KV store. Never trust the client to provide the challenge.
• Where possible, bind the challenge to the ceremony type (registration vs authentication), the user, and the expected rpId/origin.
• Issuing a new challenge should invalidate any prior outstanding challenge for the same session/operation.

Challenge Storage (Cookies)

If using cookies to store challenges (like the Hono example):

• HttpOnly: true to prevent JavaScript access.
• Secure: true so it's only sent over HTTPS.
• SameSite: 'Lax' (or 'Strict' if UX allows).
• Path: '/' or scoped narrowly to ceremony endpoints.
• Short maxAge matching your challenge TTL.
• Signed cookies prevent tampering but not reading. Challenge secrecy isn't critical, but cookie theft enables replay within TTL, so keep TTLs short.

User Identity

• user.id must be a stable, opaque, non-PII identifier (raw bytes, ≤64 bytes). Don't use email or username directly as the user handle since this leaks PII to authenticators.
• Reuse the same user.id for the account across registrations.

Registration

• Explicitly set userVerification: 'required' for passkey-grade assurance. Don't rely on defaults since they may vary across libraries and spec versions.
• Set attestation: 'none' unless you have a specific business need for device provenance. Attestation validation is complex and easy to get wrong.
• Use excludeCredentialIds to prevent duplicate registration with the same authenticator.
• If registering a credential for an existing account, require an authenticated session. Otherwise an attacker could attach their passkey to a victim's account.

Authentication

• Explicitly set userVerification: 'required'.
• allowCredentials flow (username-first): set credentialId to scope the browser prompt. Account enumeration risk comes from whether the server reveals "user exists", so mitigate with generic responses and rate limiting.
• Discoverable credentials (passkey-first): omit credentialId and map response.id to a user server-side.

Session Management

• Rotate the session ID on auth. After successful verification, mint a new session and invalidate the old one to prevent session fixation.
• Session cookies: HttpOnly, Secure, SameSite, shortest acceptable TTL.
• For sensitive actions, require recent WebAuthn verification (e.g. within 5 minutes).
• Logout:
  • Stateful sessions (session ID mapped to server-side record): invalidate the record, not just the cookie.
  • Stateless sessions (signed cookie): deleting the cookie is the only option. Stolen cookies remain valid until expiry. Consider a server-side revocation list for high-security apps.

CORS & CSRF

• Lock down CORS on ceremony endpoints. Don't use Access-Control-Allow-Origin: * with credentials.
• If your frontend and API are on different origins, allowlist exact origins and require CSRF tokens (double-submit cookie or server-stored). SameSite cookies alone are not sufficient for cross-origin credentialed requests.

Clickjacking

• Set Content-Security-Policy: frame-ancestors 'none' (or a strict allowlist) on pages that initiate ceremonies.
• Consider Permissions-Policy: publickey-credentials-create=(self), publickey-credentials-get=(self) to restrict where WebAuthn can be called.

Error Handling

• Return generic errors to clients. Don't distinguish between "unknown credential" and "verification failed" for unauthenticated callers since this leaks account enumeration info. Log specifics server-side only.
• Never log raw credential responses, challenges, or session cookies.

Rate Limiting

• Rate limit all ceremony endpoints per IP and per account.
• Use progressive backoff on repeated failures.

Credential Storage

Persist per credential (minimum):

• credentialId: stable identifier
• publicKey: hex-encoded P-256 public key from Registration.verify
• userId: associated user account
• createdAt / lastUsedAt: for audit and UX

Optional (not currently exposed by webauthx, use ox/webauthn directly if needed):

• signCount: track and validate to detect cloned authenticators
• transports: for UX hints (USB, NFC, BLE, internal)
• backupEligible / backupState: for risk-scoring synced vs hardware-bound passkeys

Recovery

• Encourage multiple credentials per account so users can register multiple passkeys/devices.
• Provide a recovery path that isn't weaker than your threat model (e.g. verified email + rate limiting, or recovery codes).