secure-auth

# Secure authentication

## Step 0: Research the current security landscape (do this first)

> Security knowledge ages on a 6-12 month half-life. The recipes below were last verified on 2026-05-08; they may be stale by the time you read this. Before applying any pattern in this skill, fan out research scoped to the authentication primitive being implemented (passwords, sessions, JWT, OAuth, MFA, passkeys) so the recipes are interpreted against current authoritative sources, not against this file's snapshot.

### Default-on, with a documented skip

Run the 4-angle research below by default. Skip ONLY when ALL of these hold:

- (a) You ran this same skill on this same primitive within the last 4 hours of the current session,
- (b) That prior research surfaced no urgent advisories for the authentication primitive being implemented (passwords, sessions, JWT, OAuth, MFA, passkeys),
- (c) You log a one-line `Research skipped because <reason>` note in your response.

"I think I know" / "moving fast" / "user wants this done quickly" / "already familiar" are NOT valid skip reasons. The whole point of this preamble is that future-you should not trust this skill body's defaults until current state is checked.

### Fan out 4 subagents in parallel

Each subagent returns at most 300 words of bullets with citations. Dispatch all 4 in a single message so they run concurrently.

**Angle 1, Authoritative standards.** Have NIST / OWASP / IETF (RFCs and Internet-Drafts) / W3C / CISA published anything new about the authentication primitive being implemented (passwords, sessions, JWT, OAuth, MFA, passkeys) in the last 6-12 months? Look for: spec finalizations, deprecations, replacement specs, RFC publications, draft revisions, NIST SP updates, OWASP project version bumps. Cite by document number plus publication date.

**Angle 2, Active exploitation.** What's actively being exploited that targets the authentication primitive being implemented (passwords, sessions, JWT, OAuth, MFA, passkeys)? Pull from: CISA Known Exploited Vulnerabilities (KEV) catalog (filter to last 6-12 months), recent CVE / GHSA entries with high CVSS or in-the-wild exploitation, breach postmortems and incident reports (CSRB, vendor RCAs, security-vendor research). Surface CWE patterns dominating recent KEV adds. Cite by CVE number plus advisory URL.

**Angle 3, Tooling and library state.** Are the libraries this skill recommends still current? What are the latest major versions in the relevant package registry (npm / PyPI / RubyGems / crates.io)? Have any been deprecated, replaced, or merged into another project? Have any flipped a secure default? Look up current versions in: registry.npmjs.org, pypi.org, rubygems.org, crates.io, pkg.go.dev. Cite by package plus version plus release date.

**Angle 4, Practitioner discourse.** What are practitioners and security teams talking about in the last 6 months? Pull from: OWASP Cheat Sheet Series (last-modified date matters), GitHub Security Lab posts, vendor security blogs (Cloudflare, Fastly, Snyk, Datadog, Wiz, GitGuardian), conference talks (Black Hat, DEF CON, OWASP Global AppSec, USENIX Security), SANS ISC, Krebs, recent OWASP project re-releases. Surface the patterns being adopted and the anti-patterns being called out. Cite by post URL plus author plus date.

### Synthesize before applying recipes

After the 4 returns land, write a 1-paragraph "current state for the authentication primitive being implemented (passwords, sessions, JWT, OAuth, MFA, passkeys), as of <today's date>" that names:

- The current normative ceiling (what specs say SHOULD be the default in 2026).
- 1-2 active threats specific to the authentication primitive being implemented (passwords, sessions, JWT, OAuth, MFA, passkeys) from the last 6-12 months.
- Any tooling drift (deprecated lib, new default in a framework, package merged or replaced).
- Any practitioner consensus shift visible in recent cheat sheet / blog updates.

If the synthesis flags drift in this skill body's recipes (e.g., a spec finalized after 2026-05-08, a library now deprecated, a default flipped), call that out explicitly in your response and override the skill body where they conflict. The synthesis wins. The skill body is scaffolding, not scripture.

### When you cannot run subagents

If subagents are not available in your runtime, the same shape applies in-line: do 4 sequential targeted searches (web search for standards, KEV catalog lookup, package registry version checks, recent cheat-sheet diff). Land the same 1-paragraph synthesis. Cost goes up; the protection does not change.

---

Production-ready authentication patterns. These aren't the simplest implementations, they're the ones that won't get you sued.

## Authentication architecture decision

The 2020-era "session vs JWT" frame is no longer the only axis. In 2026 the question is closer to "passkey plus short-lived bound tokens" vs "session cookie." Pick by deployment shape, not by what a tutorial used.

### Sessions

Use sessions when:
- Server-rendered application
- Need immediate logout / revocation
- Single domain
- Simpler to implement correctly

### JWTs (with refresh tokens)

Use JWTs when:
- Multiple services need to verify auth
- Stateless verification preferred (with revocation strategy)
- Mobile app plus API
- Third-party integrations
- High-value APIs benefit from sender-constrained tokens (DPoP per RFC 9449, mTLS per RFC 8705)

### Passkeys-first

Use passkeys (WebAuthn / FIDO2) as the primary factor when:
- The user agent supports WebAuthn (every current Chromium, Firefox, Safari, and major mobile browser does)
- You can run alongside passwords during transition (offer passkey enrollment after first login, keep password as fallback while user installs)
- Phishing resistance is required (NIST AAL3, government, financial, medical)

The passkey-first stance reflects 2026 consensus: WebAuthn L3 reached W3C Candidate Recommendation Snapshot 2026-01-13 (https://www.w3.org/TR/