auth-securitylisted

<!-- Native skill bundle for Claude Code. Generated by `secure-vibe dev regenerate`. --> <!-- Do not edit by hand; the source of truth is skills/auth-security/SKILL.md. --> # Authentication & Authorization Security JWT, OAuth 2.0 / OIDC, session management, CSRF, password hashing, and MFA enforcement ## ALWAYS - For JWT verification, pin the expected algorithm (`RS256`, `EdDSA`, or `ES256`) and verify `iss`, `aud`, `exp`, `nbf`, and `iat`. Reject `alg=none` and any unexpected algorithm. - For OAuth 2.0 public clients (SPA / mobile / CLI), use the **authorization code flow with PKCE** (S256). Never the implicit flow. Never the resource owner password credentials grant. - Cookies for sessions: `Secure; HttpOnly; SameSite=Lax` (or `Strict` for sensitive flows). Use the `__Host-` prefix when there's no subdomain sharing. - Rotate the session identifier on login and on privilege change. Bind the session to the user agent only as a soft signal — never as the sole check. - Hash passwords with argon2id (m=64 MiB, t=3, p=1) and a per-user random salt. Bcrypt cost ≥ 12 or scrypt N≥2^17 are acceptable alternatives for legacy systems. PBKDF2-SHA256 requires ≥ 600,000 iterations (OWASP 2023 minimum). - Enforce password length ≥ 12 characters with no composition rules; allow Unicode; check candidate passwords against a known-breached list (HIBP / pwned-passwords k-anonymity API). - Implement account lockout *or* rate limiting for password attempts (NIST SP 800-63B §5.2.2: at most 100 f