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    Repair WebAuthn Challenge Flow Bugs

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    Repair WebAuthn/passkey challenge-flow bugs involving challenge ownership, RP ID/origin checks, credential/user binding, concurrent tabs, one-time consumption, counters, retries, and registration/authentication mixups.

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    Repair WebAuthn Challenge Flow Bugs

    Repair WebAuthn Challenge Flow Bugs

    Example session with this skill installed

    Our passkey app stores one challenge per user session. Opening registration in one tab and login in another overwrites it, and callbacks are identified only by session. Repair with a fake WebAuthn verifier and preserve RP ID/origin and attestation policy.

    • Read your context and instructions
    • Compiled the repair webauthn challenge

    Registration and authentication share a singleton challenge instead of separate transactions. The repair stores a unique typed transaction containing challenge, RP/user context, ceremony type, expiry, and one-time state; callbacks consume exactly one transaction and tests cover two tabs, replay, wrong RP/origin, timeout, and credential/user mismatch.

    Connects securely to your tools. The creator never sees your data.

    About this skill

    The problem

    WebAuthn and passkey implementations often suffer from race conditions, inconsistent state ownership between registration and authentication, or broken cleanup logic during timeouts. These bugs lead to sporadic authentication failures that are difficult to reproduce and debug in local environments.

    What it does

    • Identifies and patches inconsistencies in WebAuthn challenge generation, storage, and one-time consumption logic.
    • Enforces strict RP ID and origin policy boundaries across parsing and validation layers.
    • Corrects sign-counter policy drift and credential-to-user binding defects.
    • Implements deterministic local fixtures and byte-level test barriers to replicate edge cases.
    • Aligns retries, cancellation, and observability without leaking customer secrets or PII.

    Frameworks & tools

    Works with any stack using WebAuthn/FIDO2 standards. Analyzes repository files via Read, Edit, and Bash.

    Why this beats prompting it yourself

    Generic prompts often suggest weakening security policies or using broad retries to "fix" flaky tests. This skill enforces transaction integrity and strictly preserves attestation and timeout policies while ensuring validation happens before irreversible state mutations.

    Use cases

    • Fixing concurrent tab conflicts where one session invalidates another's passkey challenge.
    • Repairing sign-counter synchronization issues between the authenticator and the backend.
    • Hardening registration flows to prevent partial state creation on failed attestation.
    • Adding redacted observability to track passkey failures without logging sensitive credentials.

    Known limitations

    Cannot contact production services or access live customer data. Requires local repository access and operates through disposable fixtures rather than live hardware authenticators.

    Find more skills like this on the Claude Skills Marketplace, the Codex Skills Marketplace and the Gemini Skills Marketplace, or browse Claude Skills for Agents & Orchestration.

    Cannot redesign RP ID/origin policy, attestation policy, authenticator requirements, account-recovery policy, sign-counter policy, timeout policy, and public errors; cannot verify production infrastructure or prove every runtime, proxy, network, filesystem, or scheduler ordering.

    How to use

    1. 1

      Connect your agent to the Agensi MCP

      Copy the prompt and paste it into Claude, ChatGPT, Cursor or any agent that supports MCP. It sets up the connection for you. Manual setup

    2. 2

      Sign in to Agensi

      Your agent shows a sign-in link. Sign in and click Allow.

    3. 3

      Ask for what you need

      Your agent loads this skill and uses it on your task. It always asks before buying a skill.

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    Security scan passed 2 months ago

    Permissions

    Terminal / Shell
    Read Files
    Write Files

    Run on a clean branch with repository files and disposable local fixtures. Review patches and validation before merge. Keep production services, real credentials, customer payloads, and deployment out of scope.

    Listed2 months ago
    Updated8 days ago

    What's inside

    Frequently Asked Questions

    This skill addresses complex, state-dependent bugs like sign-counter drift, concurrent session conflicts, and RP ID/origin mismatches that standard AI prompts often fail to resolve securely.

    The skill is compatible with any AI agent capable of file-system operations (Read, Edit, Bash) and works across all major backend frameworks implementing FIDO2 standards.

    No, the skill utilizes deterministic local fixtures and byte-level test barriers to simulate authentication flows, ensuring your code is tested without needing physical security keys.

    The skill identifies and patches logic errors while strictly enforcing WebAuthn security policies, ensuring that fixes do not accidentally weaken your attestation or timeout protections.

    You receive the complete skill package including logic for challenge ownership repair, origin validation hardening, and specialized observability templates for tracking passkey failures.

    New in Agents & Orchestration