Authentication security

Authentication Security

Purpose

Assess whether the system's identity handling resists attack: are credentials stored safely, tokens/sessions handled correctly, flows enumeration- and brute-force-resistant, and revocation real. The review/audit lens; the design and construction live in ../../backend/backend-authentication.

When to Use

• Reviewing authentication design or an existing implementation for security.
• As the identity slice of ../../security-review and threat-modeling spoofing/elevation threats.
• Not for building auth (../../backend/backend-authentication) or authorization (authorization-security).

Inputs

• The authentication design/implementation (../../backend/backend-authentication).
• Threat model's identity threats (threat-modeling).

Discovery Questions

• How are passwords stored (adaptive hash?), and are secrets/tokens ever logged?
• Session vs JWT — is revocation actually possible, and does logout/password-change invalidate?
• Are login/reset flows resistant to brute force (abuse-prevention) and account enumeration?
• Are reset tokens/OTPs single-use, expiring, and attempt-limited? Is MFA (if present) implemented soundly?

Responsibilities

• Verify credential storage: adaptive hashing (bcrypt/argon2/scrypt), never plaintext or fast hashes; no credentials/tokens in logs, errors, or URLs.
• Assess session/token handling: httpOnly/secure/sameSite cookies for browsers (not localStorage tokens); short-lived access + rotating refresh with reuse detection for JWTs; signing keys managed (secrets-audit).
• Verify revocation is real: logout and password change invalidate sessions/tokens; a pure-stateless JWT with no denylist can't truly revoke — flag the gap.
• Check brute-force + enumeration resistance: login/reset/OTP throttled and CAPTCHA-guarded (abuse-prevention); responses don't reveal whether an account exists.
• Review flows: reset tokens single-use + expiring; OTP attempt-limited + expiring; MFA/recovery-code secrets stored safely; verification flows sound.
• Confirm findings become security regression tests (security-regression-testing).

Required Workflow

1. Review credential storage + secret handling.
2. Assess session/token issuance, expiry, rotation, revocation.
3. Check brute-force + enumeration resistance on public flows.
4. Review reset/OTP/MFA flows for reuse/expiry/limits.
5. Record findings (Confirmed vs Potential); route mitigations to build skills + regression tests.

Decision Rules

• Fast-hash or plaintext passwords = confirmed high-severity finding.
• If revocation is required but the token scheme can't do it, that's a design finding, not a nitpick.
• Enumeration-revealing responses on login/reset are real findings — attackers harvest valid accounts.
• Client-held auth state is a hint, never proof; server must verify every request.

Rules

• Never print discovered secrets/credentials — reference location, flag rotation (secrets-audit).
• Findings separated Confirmed vs Potential; never declare auth "secure" (../../security-review).
• Each finding maps to a fix + a regression test.

Anti-Patterns

• Reviewing auth as if "logged in" implied "authorized" (that's authorization-security).
• Passing an implementation with unrevocable long-lived tokens.
• Ignoring account enumeration in error messages/timing.
• Reset links that don't expire or reused OTPs.
• Treating rate limiting as the whole brute-force defense (it's one layer).

Validation Checklist

• Credential storage: adaptive hashing; no secret logging.
• Session/token: secure cookies / rotating refresh; keys managed.
• Revocation real (logout/password-change invalidate).
• Brute-force + enumeration resistance verified.
• Reset/OTP/MFA flows: single-use, expiring, attempt-limited.
• Findings → fixes → regression tests.

Definition of Done

A recorded authentication security assessment — credential storage, session/token handling, revocation, brute-force/enumeration resistance, and account flows — with Confirmed/Potential findings routed to fixes and security regression tests, and no "secure" claim.

Related Skills

../../backend/backend-authentication, authorization-security, abuse-prevention, secrets-audit, security-regression-testing, ../../security-review, threat-modeling, web-security, mobile-security.

Related Knowledge

../../../knowledge/ (identity threats, provider constraints).

Related References

../../../references/security/ (auth review checklists, when populated).

Context Loading Guidance

• Requires: the authentication design/impl, identity threats.
• Does not require: authorization model, unrelated code.
• May load: ../../backend/backend-authentication, abuse-prevention.
• Stop when: findings + routed mitigations/regression tests are recorded.

Token Efficiency Guidance

The finding table (area → issue → severity → fix → test) is the artifact; never echo real credentials/secrets.