Authentication, MFA & Session Management

description: Authentication, MFA, and Session Management (passwords, MFA, OAuth/OIDC, SAML, sessions, cookies) languages:

• c
• go
• java
• javascript
• kotlin
• php
• python
• ruby
• swift
• typescript alwaysApply: false

rule_id: codeguard-0-authentication-mfa

Authentication, MFA & Session Management

Build a resilient, user-friendly authentication system that resists credential attacks, protects secrets, supports strong MFA, and implements secure session handling.

Part 1: Authentication & MFA

Account Identifiers and UX

• Use non-public, random, and unique internal user identifiers. Allow login via verified email or username.
• Always return generic error messages (e.g., "Invalid username or password"). Keep timing consistent to prevent account enumeration.
• Support password managers: <input type="password">, allow paste, no JS blocks.

Password Policy

• Accept passphrases and full Unicode; minimum 8 characters; avoid composition rules. Set only a reasonable maximum length (64+).
• Check new passwords against breach corpora (e.g., k‑anonymity APIs); reject breached/common passwords.

Password Storage (Hashing)

• Hash, do not encrypt. Use slow, memory‑hard algorithms with unique per‑user salts and constant‑time comparison.
• Preferred order and parameters (tune to your hardware; target <1s on server):
  • Argon2id: m=19–46 MiB, t=2–1, p=1 (or equivalent security trade‑offs)
  • scrypt: N=2^17, r=8, p=1 (or equivalent)
  • bcrypt (legacy only): cost ≥10, be aware of 72‑byte input limit
  • PBKDF2 (FIPS): PBKDF2‑HMAC‑SHA‑256 ≥600k, or SHA‑1 ≥1.3M
• Optional pepper: store outside DB (KMS/HSM); if used, apply via HMAC or pre‑hashing. Plan for user resets if pepper rotates.
• Unicode and null bytes must be supported end‑to‑end by the library.

Authentication Flow Hardening

• Enforce TLS for all auth endpoints and token transport; enable HSTS.
• Implement rate limits per IP, account, and globally; add proof‑of‑work or CAPTCHA only as last resort.
• Lockouts/throttling: progressive backoff; avoid permanent lockout via resets/alerts.
• Uniform responses and code paths to reduce oracle/timing signals.

Multi‑Factor Authentication (MFA)

• Adopt phishing‑resistant factors by default for sensitive accounts: passkeys/WebAuthn (FIDO2) or hardware U2F.
• Acceptable: TOTP (app‑based), smart cards with PIN. Avoid for sensitive use: SMS/voice, email codes; never rely on security questions.
• Require MFA for: login, password/email changes, disabling MFA, privilege elevation, high‑value transactions, new devices/locations.
• Risk‑based MFA signals: new device, geo‑velocity, IP reputation, unusual time, breached credentials.
• MFA recovery: provide single‑use backup codes, encourage multiple factors, and require strong identity verification for resets.
• Handle failed MFA: offer alternative enrolled methods, notify users of failures, and log context (no secrets).

Federation and Protocols (OAuth 2.0 / OIDC / SAML)

• Use standard protocols only; do not build your own.
• OAuth 2.0/OIDC:
  • Prefer Authorization Code with PKCE for public/native apps; avoid Implicit and ROPC.
  • Validate state and nonce; use exact redirect URI matching; prevent open redirects.
  • Constrain tokens to audience/scope; use DPoP or mTLS for sender‑constraining when possible.
  • Rotate refresh tokens; revoke on logout or risk signals.
• SAML:
  • TLS 1.2+; sign responses/assertions; encrypt sensitive assertions.
  • Validate issuers, InResponseTo, timestamps (NotBefore/NotOnOrAfter), Recipient; verify against trusted keys.
  • Prevent XML signature wrapping with strict schema validation and hardened XPath selection.
  • Keep response lifetimes short; prefer SP‑initiated flows; validate RelayState; implement replay detection.

Tokens (JWT and Opaque)

• Prefer opaque server‑managed tokens for simplicity and revocation. If using JWTs:
  • Explicitly pin algorithms; reject "none"; validate iss/aud/exp/iat/nbf; use short lifetimes and rotation.
  • Store secrets/keys securely (KMS/HSM). Use strong HMAC secrets or asymmetric keys; never hardcode.
  • Consider binding tokens to a client context (e.g., fingerprint hash in cookie) to reduce replay.
  • Implement denylist/allowlist for revocation on logout and critical events.

Recovery and Reset

• Return the same response for existing and non‑existing accounts (no enumeration). Normalize timing.
• Generate 32+ byte, CSPRNG tokens; single‑use; store as hashes; short expiry.
• Use HTTPS reset links to pinned, trusted domains; add referrer policy (no‑referrer) on UI.
• After reset: require re‑authentication, rotate sessions, and do not auto‑login.
• Never lock accounts due to reset attempts; rate‑limit and monitor instead.

Administrative and Internal Accounts

• Separate admin login from public forms; enforce stronger MFA, device posture checks, IP allowlists, and step‑up auth.
• Use distinct session contexts and stricter timeouts for admin operations.

Part 2: Session Management & Cookies

Session ID Generation and Properties

• Generate session IDs with a CSPRNG; ≥64 bits of entropy (prefer 128+). Opaque, unguessable, and free of meaning.
• Use generic cookie names (e.g., id) rather than framework defaults. Reject any incoming ID not created by the server.
• Store all session data server-side; never embed PII or privileges in the token. If sensitive, encrypt server-side session store at rest.

Cookie Security Configuration

• Set Secure, HttpOnly, SameSite=Strict (or Lax if necessary for flows) on session cookies.
• Scope cookies narrowly with Path and Domain. Avoid cross-subdomain exposure.
• Prefer non-persistent session cookies (no Expires/Max-Age). Require full HTTPS; enable HSTS site-wide.

Example header:

Set-Cookie: id=<opaque>; Secure; HttpOnly; SameSite=Strict; Path=/

Session Lifecycle and Rotation

• Create sessions only server-side; treat provided IDs as untrusted input.
• Regenerate session ID on authentication, password changes, and any privilege elevation. Invalidate the prior ID.
• Use distinct pre‑auth and post‑auth cookie names if framework patterns require it.

Expiration and Logout

• Idle timeout: 2–5 minutes for high-value, 15–30 minutes for lower risk. Absolute timeout: 4–8 hours.
• Enforce timeouts server-side. Provide a visible logout button that fully invalidates the server session and clears the cookie client-side.

Transport and Caching

• Enforce HTTPS for the entire session journey. Never mix HTTP/HTTPS in one session.
• Send Cache-Control: no-store on responses containing session identifiers or sensitive data.

Cookie Theft Detection and Response

• Fingerprint session context server-side at establishment (IP, User-Agent, Accept-Language, relevant sec-ch-ua where available).
• Compare incoming requests to the stored fingerprint, allowing for benign drift (e.g., subnet changes, UA updates).
• Risk-based responses:
  • High risk: require re-authentication; rotate session ID.
  • Medium risk: step-up verification (challenge); rotate session ID.
  • Low risk: log suspicious activity.
• Always regenerate the session ID when potential hijacking is detected.

Client-Side Storage

• Do not store session tokens in localStorage/sessionStorage due to XSS risk. Prefer HttpOnly cookies for transport.
• If client-side storage is unavoidable for non-session secrets, isolate via Web Workers and never expose in page context.

Framework and Multi-Cookie Scenarios

• Prefer built-in session frameworks; keep them updated and hardened.
• Validate relationships when multiple cookies participate in session state; avoid same cookie names across paths/domains.

Monitoring and Telemetry

• Log auth events (failures/successes, MFA enroll/verify, resets, lockouts) with stable fields and correlation IDs; never log secrets or raw tokens.
• Log session lifecycle events (creation, rotation, termination) using salted hashes of the session ID, not raw values.
• Detect credential stuffing: high failure rates, many IPs/agents, impossible travel. Notify users of new device logins.
• Monitor for brute force of session IDs and anomalous concurrent usage.

Implementation Checklist

Authentication

• Passwords: Argon2id (preferred) with per‑user salt, constant‑time verify; breached password checks on change/set.
• MFA: WebAuthn/passkeys or hardware tokens for high‑risk; TOTP as fallback; secure recovery with backup codes.
• Federation: Authorization Code + PKCE; strict redirect URI validation; audience/scope enforced; token rotation.
• Tokens: short‑lived, sender‑constrained where possible; revocation implemented; secrets in KMS/HSM.
• Recovery: single‑use, hashed, time‑boxed tokens; consistent responses; re‑auth required after reset; sessions rotated.
• Abuse: rate limits, throttling, and anomaly detection on auth endpoints; uniform error handling.
• Admin: isolated flows with stricter policies and device checks.

Session Management

• CSPRNG session IDs (≥64 bits entropy), opaque and server-issued only.
• Cookie flags: Secure, HttpOnly, SameSite set; tight domain/path.
• HTTPS-only with HSTS; no mixed content.
• Regenerate IDs on auth and privilege changes; invalidate old IDs.
• Idle and absolute timeouts enforced server-side; full logout implemented.
• Cache-Control: no-store for sensitive responses.
• Server-side fingerprinting and risk-based responses to anomalies.
• No client storage of session tokens; framework defaults hardened.

Test Plan

• Unit/integration tests for login, MFA enroll/verify, resets, and lockouts with uniform errors.
• Protocol tests: PKCE, state/nonce, redirect URI validation, token audience/scope.
• Dynamic tests for credential stuffing resistance and token replay; validate revocation after logout and role change.
• Session ID entropy validation; cookie attribute verification.
• Session fixation and hijacking scenario tests.

OWASP References

• Authentication_Cheat_Sheet.md
• Password_Storage_Cheat_Sheet.md
• Multifactor_Authentication_Cheat_Sheet.md
• Session_Management_Cheat_Sheet.md
• Cookie_Theft_Mitigation_Cheat_Sheet.md
• Forgot_Password_Cheat_Sheet.md
• OAuth2_Cheat_Sheet.md
• SAML_Security_Cheat_Sheet.md
• JSON_Web_Token_for_Java_Cheat_Sheet.md