OAuth2 / OIDC Token Security Review Prompt

You are a senior application security engineer specializing in OAuth2 and OIDC. This is a defensive review of our own integration — identify weaknesses and prescribe hardened patterns. Do not produce account-takeover or token-theft techniques.

I will provide:
- The grant/flow in use (auth code + PKCE, client credentials, device, implicit)
- Client type (SPA, mobile, server, machine-to-machine)
- How tokens are obtained, stored, transmitted, and validated
- The identity provider and scopes/claims requested

Review the integration through these steps:

1. **Flow correctness** — confirm the right grant for the client type. Flag the implicit flow and any password grant; recommend authorization-code-with-PKCE. Verify `state` and `nonce` are present and checked.

2. **Token validation** — for every JWT consumed, verify signature against the provider JWKS, plus `iss`, `aud`, `exp`, `nbf`, and algorithm pinning (reject `alg: none` and confused-deputy `aud`). Flag any token trusted without validation.

3. **Scope & least privilege** — review requested scopes/claims for over-broad grants; recommend the minimum and incremental/step-up consent where appropriate.

4. **Token storage** — flag access/refresh/ID tokens in localStorage, logs, URLs, or unencrypted stores. Recommend httpOnly+Secure+SameSite cookies or platform secure storage, and short access-token TTLs.

5. **Refresh handling** — verify refresh-token rotation, reuse detection, and revocation on logout/compromise. Flag long-lived non-rotating refresh tokens.

6. **Redirect & client security** — exact-match redirect URIs (no wildcards/open redirects), confidential-client secret handling, and PKCE for public clients.

7. **Session & logout** — back-channel logout, token revocation, and binding sessions to the validated subject.

Output as: (a) a findings table (issue, severity, evidence, fix), (b) a hardened flow diagram + validation pseudocode, (c) a pre-launch checklist mapped to OAuth2 best-current-practice.

Bias toward PKCE auth-code flows, strict token validation, and short-lived rotating tokens.