SkillVaultskills Browse all 500 skills

Security · Version 1.3.0 · Reviewed 2026-08-02

WebAuthn & Passkey Advisor

Find and prioritize exploitable risk in passkey flow design and credential recovery with evidence, explicit trade-offs, and a verification plan.

4 method steps 6 documented failure modes 5 diagnostic checks 7 quality gates

Designs passkey registration and authentication with relying-party IDs, origins, attestation, discoverable credentials, recovery, and sync considerations.

₹99 one-time

Get this skill archive

What this skill helps you do

  • Passkey flow design
  • Credential recovery
  • WebAuthn verification review

How WebAuthn & Passkey Advisor works

You provide

Flow diagram, token config, and authorization code

It inspects

Claim validation and enforcement point for passkey flow design

It decides

A credential recovery design that fails closed

You verify

Cross-tenant request with a valid token is rejected

What it checks first

WebAuthn & Passkey Advisor designs passkey registration and authentication with relying-party IDs, origins, attestation, discoverable credentials, recovery, and sync considerations. Use it when the work involves Passkey flow design, Credential recovery, WebAuthn verification review.

  1. Where the token is validated and whether the signature, issuer, audience, and expiry are all checked.
  2. Token lifetime relative to the revocation requirement, since a long-lived token cannot be revoked without a check.
  3. Whether authorization is evaluated at the data layer or only at the route.
  4. Token storage location, which determines exposure to XSS versus CSRF.
  5. Whether the flow uses PKCE and validates `state`, which decides interception and CSRF resistance.

Failure modes it recognizes

  • Accepting a JWT with `alg: none` or verifying with the wrong key type, allowing forged tokens.
  • Validating signature but not `aud`, allowing a token minted for another service to be replayed.
  • Refresh tokens without rotation or reuse detection, so a stolen token remains valid indefinitely.
  • Session fixation from not regenerating the session identifier after privilege change.
  • Role checks in the UI only, with the API trusting a client-supplied role claim.
  • Redirect URI matched by prefix rather than exact value, enabling token exfiltration.

Answers it will reject

  • Building a custom authentication protocol instead of using a reviewed standard implementation.
  • Storing access tokens in `localStorage` while claiming XSS is out of scope.
  • Using long-lived API keys where short-lived scoped credentials are available.
  • Treating authentication as sufficient for authorization, which is the most common access-control defect.

Decision rules it applies

  • Authorize at the point of data access, because every route eventually gets a second caller.
  • Prefer short-lived access tokens with rotating refresh tokens and reuse detection.
  • Match redirect URIs exactly and require PKCE for every public client.
  • Fail closed: an unparseable or unverifiable token is a rejection, never a fallback to anonymous.

Evidence it asks for

  • Decode a real token and verify each claim check exists in code: signature, issuer, audience, expiry, and not-before.
  • Test horizontal access by requesting another tenant's resource with a valid token.
  • Confirm revocation actually terminates access within the documented window.

The method inside

  1. Map the artifact, actors, boundaries, and invariants relevant to passkey flow design.
  2. Trace concrete failure or abuse paths for credential recovery; do not report checklist items without a mechanism.
  3. Prioritize WebAuthn verification review findings by impact, likelihood, confidence, and cost of correction.
  4. Recommend the smallest defensible change, then define how an independent reviewer can verify it.

Deliverables

  • Passkey flow design assessment
  • Credential recovery decision and action plan
  • WebAuthn verification review verification checklist

Evidence requirements

  • Code, configuration, data flows, and trust boundaries
  • Identity, authorization, and deployment context
  • Threat model, controls, and known assumptions

Quality gates

  • Every material claim traces to supplied evidence or is labeled as a hypothesis.
  • The response follows the declared deliverable contract.
  • No execution, access, measurement, or verification is invented.
  • Secrets and personal data are redacted rather than repeated.
  • The user receives a concrete independent verification step.
  • The relevant failure modes in this domain were considered rather than only the reported symptom.
  • No listed anti-pattern was recommended as a solution.

Example task

Input

Add passkeys to our multi-domain product without locking users out when they change devices.

Expected output

Choose the registrable parent as RP ID only if every approved origin is under it, support discoverable credentials, and design account recovery independently because passkey synchronization varies by ecosystem...

Boundaries and compatibility

Ideal for

  • Passkey flow design: produce a decision or artifact grounded in supplied evidence.
  • Credential recovery: produce a decision or artifact grounded in supplied evidence.
  • WebAuthn verification review: produce a decision or artifact grounded in supplied evidence.

Out of scope

  • Authorizing offensive actions against systems without permission
  • Reporting theoretical issues as exploitable without a path

Agent compatibility

  • GitHub Copilot custom agents
  • Claude Agent Skills / SKILL.md
  • Any instruction-following chat model

Tool policy: Advisory by default. No tools are assumed. If the host provides tools, use read-only evidence gathering unless the user explicitly approves a scoped write or execution action.