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    Repair OAuth PKCE Flow Mixups

    1

    Repair OAuth PKCE and authorization-flow mixups where state, nonce, redirect URI, code verifier, provider, tenant, session, or browser tab are matched to the wrong transaction.

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    Repair OAuth PKCE Flow Mixups

    Repair OAuth PKCE Flow Mixups

    Example session with this skill installed

    Our TypeScript app stores one oauth_state and pkce_verifier per session. Starting Google login in one tab and Microsoft login in another overwrites both; the first callback can consume the second verifier. Repair with a fake IdP and controlled callbacks. Preserve providers, redirect allowlists, S256 PKCE, nonce, timeouts, token handling, and errors.

    • Read your context and instructions
    • Compiled the repair oauth pkce

    Authorization-transaction mixup found. Session-global state and verifier fields are overwritten by the newest tab, so callbacks are not bound to provider, redirect URI, or initiation generation. The repair creates one opaque transaction record per state, binds provider/tenant/redirect/nonce/verifier, consumes it atomically once, preserves S256 and all validation/token/error policy, and proves concurrent-tab, replay, timeout, and wrong-provider rejection with a fake IdP.

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

    About this skill

    The problem

    Race conditions and session-scoped state often cause OAuth flows to collide when users open multiple tabs or retry logins. This leads to code_verifier mismatches, provider identity loss, and corrupted authorization transactions that are notoriously difficult to debug in production.

    What it does

    • Identifies where concurrent OAuth transactions overwrite shared session state or PKCE verifiers.
    • Enforces strict ownership between callbacks, cached state, and the specific transaction generation.
    • Fixes redirect URI mismatches between the authorization and token exchange phases.
    • Implements deterministic local IdP fakes to reproduce concurrency bugs without live secrets.
    • Redacts sensitive observability data while improving metrics for terminal failure reasons.

    Frameworks & tools

    Works with any repository using OAuth 2.0, OIDC, and PKCE. Compatible with Bash, Read, and Edit toolsets for codebase patching.

    Why this beats prompting it yourself

    General LLMs often suggest insecure workarounds like increasing timeouts or loosening validation. This skill follows a mandatory safety discipline that preserves strict PKCE and OIDC specs while fixing the underlying state synchronization logic.

    Use cases

    • Fixing "invalid_grant" errors caused by multiple browser tabs overwriting session cookies.
    • Correcting flows where a callback for Provider A inadvertently attempts to resume a flow for Provider B.
    • Ensuring one-time state consumption to prevent replay or reuse of authorization codes.
    • Patching mismatched redirect_uri parameters across complex multi-tenant environments.

    Known limitations

    Requires access to repository files to perform analysis. Cannot interact with production services or read live secrets.

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

    Cannot choose or change OAuth/OIDC validation, PKCE method, redirect allowlist, provider/tenant policy, token handling, timeout, retry, and public errors; cannot verify production infrastructure or prove every runtime, proxy, network, 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

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      Sign in to Agensi

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    3. 3

      Ask for what you need

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    Permissions

    Terminal / Shell
    Read Files
    Write Files

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

    Listed2 months ago
    Updated9 days ago

    What's inside

    Frequently Asked Questions

    This skill identifies and patches race conditions where concurrent OAuth transactions—such as multiple open tabs or retried logins—overwrite shared session state or PKCE verifiers. It enforces strict ownership between callbacks and specific transaction IDs to prevent common 'invalid_grant' errors.

    The skill is designed for any AI agent with repository access and file manipulation capabilities (like Bash, Read, and Edit). It works across any language or framework implementing OAuth 2.0 and OIDC, including Node.js, Python, and Go environments.

    No, this skill is strictly for codebase analysis and patching; it cannot access production environments, live databases, or sensitive secrets. It uses deterministic local IdP fakes to safely reproduce and fix concurrency bugs within your development environment.

    You receive the specialized logic for diagnosing OAuth state mixups and the corrective patching strategies for PKCE and OIDC flows. This includes the ability to fix redirect URI mismatches and implement secure state-consumption logic.

    Unlike general prompts that might suggest loosening validation, this skill follows a safety-first approach that maintains strict PKCE and OIDC specifications. It prioritizes fixing the underlying state synchronization logic rather than applying insecure workarounds like extended timeouts.

    New in APIs & Backend