Securing Authentication Agent Skill

Authentication & Security

Implement modern authentication, authorization, and API security across Python, Rust, Go, and TypeScript.

When to Use This Skill

Use this skill when:

• Building user authentication systems (login, signup, SSO)
• Implementing authorization (roles, permissions, access control)
• Securing APIs (JWT validation, rate limiting)
• Adding passwordless auth (Passkeys/WebAuthn)
• Migrating from password-based to modern auth
• Integrating enterprise SSO (SAML, OIDC)
• Implementing fine-grained permissions (RBAC, ABAC, ReBAC)

OAuth 2.1 Mandatory Requirements (2025 Standard)

┌─────────────────────────────────────────────────────────────┐
│           OAuth 2.1 MANDATORY REQUIREMENTS                  │
│                   (RFC 9798 - 2025)                         │
├─────────────────────────────────────────────────────────────┤
│                                                             │
│  ✅ REQUIRED (Breaking Changes from OAuth 2.0)             │
│  ├─ PKCE (Proof Key for Code Exchange) MANDATORY           │
│  │   └─ S256 method (SHA-256), minimum entropy 43 chars   │
│  ├─ Exact redirect URI matching                            │
│  │   └─ No wildcard matching, no substring matching       │
│  ├─ Authorization code flow ONLY for public clients       │
│  │   └─ All other flows require confidential client       │
│  └─ TLS 1.2+ required for all endpoints                   │
│                                                             │
│  ❌ REMOVED (No Longer Supported)                          │
│  ├─ Implicit grant (security vulnerabilities)             │
│  ├─ Resource Owner Password Credentials grant              │
│  │   └─ Use OAuth 2.0 Device Flow (RFC 8628) instead      │
│  └─ Bearer token in query parameters                       │
│      └─ Must use Authorization header or POST body        │
│                                                             │
└─────────────────────────────────────────────────────────────┘

Critical: PKCE is now mandatory for ALL OAuth flows, not just public clients.

JWT Best Practices

Signing Algorithms (Priority Order)

• EdDSA with Ed25519 (Recommended)
• Fastest performance
• Smallest signature size
• Modern cryptography

• ES256 (ECDSA with P-256)
• Good performance
• Industry standard
• Wide compatibility

• RS256 (RSA)
• Legacy compatibility
• Larger signatures
• Slower performance

NEVER allow alg: none or algorithm switching attacks.

Token Lifetimes (Concrete Values)

• Access token: 5-15 minutes
• Refresh token: 1-7 days with rotation
• ID token: Same as access token (5-15 minutes)

Refresh token rotation: Each refresh generates new access AND refresh tokens, invalidating the old refresh token.

Token Storage

• Access token: Memory only (never localStorage)
• Refresh token: HTTP-only cookie + SameSite=Strict
• CSRF token: Separate non-HTTP-only cookie
• Never log tokens: Redact in application logs

JWT Claims (Required)

{
  "iss": "https://auth.example.com",
  "sub": "user-id-123",
  "aud": "api.example.com",
  "exp": 1234567890,
  "iat": 1234567890,
  "jti": "unique-token-id",
  "scope": "read:profile write:data"
}

Password Hashing with Argon2id

OWASP 2025 Parameters

Algorithm: Argon2id
Memory cost (m): 64 MB (65536 KiB)
Time cost (t): 3 iterations
Parallelism (p): 4 threads
Salt length: 16 bytes (128 bits)
Target hash time: 150-250ms

Implementation

For concrete implementations, see references/password-hashing.md.

Key Points:

• Argon2id is hybrid: data-independent timing + memory-hard
• Tune memory cost to achieve 150-250ms on YOUR hardware
• Use timing-safe comparison for verification
• Migrate from bcrypt gradually (verify with old, rehash with new)

Passkeys / WebAuthn

Passkeys provide phishing-resistant, passwordless authentication using FIDO2/WebAuthn.

When to Use Passkeys

• User-facing applications prioritizing security
• Reducing password-related support burden
• Mobile-first applications (biometric auth)
• Applications requiring MFA without SMS

Cross-Device Passkey Sync

• iCloud Keychain: Apple ecosystem (iOS 16+, macOS 13+)
• Google Password Manager: Android, Chrome
• 1Password, Bitwarden: Third-party password managers

For implementation guide, see references/passkeys-webauthn.md.

Authorization Models

┌─────────────────────────────────────────────────────────────┐
│                Authorization Model Selection                │
├─────────────────────────────────────────────────────────────┤
│                                                             │
│  Simple Roles (<20 roles)                                  │
│  └─ RBAC with Casbin (embedded, any language)              │
│      Example: Admin, User, Guest                           │
│                                                             │
│  Complex Attribute Rules                                    │
│  └─ ABAC with OPA or Cerbos                                │
│      Example: "Allow if user.clearance >= doc.level        │
│                AND user.dept == doc.dept"                   │
│                                                             │
│  Relationship-Based (Multi-Tenant, Collaborative)          │
│  └─ ReBAC with SpiceDB (Zanzibar model)                    │
│      Example: "Can edit if member of doc's workspace       │
│                AND workspace.plan includes feature"         │
│      Use cases: Notion-like, GitHub-like permissions       │
│                                                             │
│  Kubernetes / Infrastructure Policies                       │
│  └─ OPA (Gatekeeper for admission control)                 │
│      Example: Enforce pod security policies                │
│                                                             │
└─────────────────────────────────────────────────────────────┘

For detailed comparison, see references/authorization-patterns.md.

Library Selection by Language

TypeScript

| Use Case | Library | Context7 ID | Trust | Notes |

|----------|---------|-------------|-------|-------|

| Auth Framework | Auth.js v5 | /websites/authjs_dev | 87.4 | Multi-framework (Next, Svelte, Solid) |

| JWT | jose 5.x | - | - | EdDSA, ES256, RS256 support |

| Passkeys | @simplewebauthn/server 11.x | - | - | FIDO2 server |

| Validation | Zod 3.x | /colinhacks/zod | 90.4 | Schema validation |

| Policy Engine | Casbin.js 1.x | - | - | RBAC/ABAC embedded |

Python

| Use Case | Library | Notes |

|----------|---------|-------|

| Auth Framework | Authlib 1.3+ | OAuth/OIDC client + server |

| JWT | joserfc 1.x | Modern, maintained |

| Passkeys | py_webauthn 2.x | WebAuthn server |

| Password Hashing | argon2-cffi 24.x | OWASP parameters |

| Validation | Pydantic 2.x | FastAPI integration |

| Policy Engine | PyCasbin 1.x | RBAC/ABAC embedded |

Rust

| Use Case | Library | Notes |

|----------|---------|-------|

| JWT | jsonwebtoken 10.x | EdDSA, ES256, RS256 |

| OAuth Client | oauth2 5.x | OAuth 2.1 flows |

| Passkeys | webauthn-rs 0.5.x | WebAuthn + attestation |

| Password Hashing | argon2 0.5.x | Native Argon2id |

| Policy Engine | Casbin-RS 2.x | RBAC/ABAC embedded |

Go

| Use Case | Library | Notes |

|----------|---------|-------|

| JWT | golang-jwt v5 | Community-maintained |

| OAuth Client | go-oidc v3 | OIDC client only |

| Passkeys | go-webauthn 0.11.x | Duo-maintained |

| Password Hashing | golang.org/x/crypto/argon2 | Standard library |

| Policy Engine | Casbin v2 | Original implementation |

Managed Auth Services

| Service | Best For | Key Features |

|---------|----------|--------------|

| Clerk | Rapid development, startups | Prebuilt UI, Next.js SDK |

| Auth0 | Enterprise, established | 25+ social providers, SSO |

| WorkOS AuthKit | B2B SaaS, enterprise SSO | SAML/SCIM, admin portal |

| Supabase Auth | Postgres users | Built on Postgres, RLS |

For detailed comparison, see references/managed-auth-comparison.md.

Self-Hosted Solutions

| Solution | Language | Use Case |

|----------|----------|----------|

| Keycloak | Java | Enterprise, on-prem |

| Ory | Go | Cloud-native, microservices |

| Authentik | Python | Modern, developer-friendly |

For setup guides, see references/self-hosted-auth.md.

API Security Best Practices

Rate Limiting

// Tiered rate limiting (per IP + per user)
const rateLimits = {
  anonymous: '10 requests/minute',
  authenticated: '100 requests/minute',
  premium: '1000 requests/minute',
}

Use sliding window algorithm (not fixed window) with Redis.

CORS Configuration

// Restrictive CORS (production)
const corsOptions = {
  origin: ['https://app.example.com'],
  credentials: true,
  maxAge: 86400, // 24 hours
  allowedHeaders: ['Content-Type', 'Authorization'],
  methods: ['GET', 'POST', 'PUT', 'DELETE', 'PATCH'],
}

// NEVER use origin: '*' with credentials: true

Security Headers

const securityHeaders = {
  'Strict-Transport-Security': 'max-age=63072000; includeSubDomains; preload',
  'X-Frame-Options': 'DENY',
  'X-Content-Type-Options': 'nosniff',
  'Referrer-Policy': 'strict-origin-when-cross-origin',
  'Permissions-Policy': 'geolocation=(), microphone=(), camera=()',
  'Content-Security-Policy': "default-src 'self'; script-src 'self'",
}

For complete API security guide, see references/api-security.md.

Frontend Integration Patterns

Protected Routes (Next.js)

// middleware.ts
import { withAuth } from 'next-auth/middleware'

export default withAuth({
  callbacks: {
    authorized: ({ token, req }) => {
      if (req.nextUrl.pathname.startsWith('/dashboard')) {
        return !!token
      }
      if (req.nextUrl.pathname.startsWith('/admin')) {
        return token?.role === 'admin'
      }
      return true
    },
  },
})

export const config = {
  matcher: ['/dashboard/:path*', '/admin/:path*'],
}

Role-Based UI Rendering

import { useSession } from 'next-auth/react'

export function AdminPanel() {
  const { data: session } = useSession()

  if (session?.user?.role !== 'admin') {
    return null
  }

  return <div>Admin Controls</div>
}

Common Workflows

1. OAuth 2.1 Integration

• Generate PKCE challenge
• Redirect to authorization endpoint
• Handle callback with authorization code
• Exchange code for tokens (with code_verifier)
• Store tokens securely
• Implement refresh token rotation

See references/oauth21-guide.md for complete implementation.

2. JWT Implementation

• Generate signing keys using scripts/generate_jwt_keys.py
• Configure token lifetimes (5-15 min access, 1-7 day refresh)
• Implement token validation middleware
• Set up refresh token rotation
• Configure token storage (memory for access, HTTP-only cookie for refresh)

See references/jwt-best-practices.md for detailed patterns.

3. Passkeys Setup

• Register credential during signup/settings
• Generate challenge for registration
• Verify attestation
• Store credential ID and public key
• Implement authentication flow with assertion

See examples/passkeys-demo/ for runnable implementation.

4. Authorization Engine Setup

• Choose engine (Casbin for simple RBAC, SpiceDB for ReBAC)
• Define schema/policies
• Implement check functions
• Integrate with route handlers
• Add audit logging

See references/authorization-patterns.md for detailed comparison.

Integration with Other Skills

Forms Skill

• Login/register forms with validation
• Error states for auth failures
• Password strength indicators
• Email validation

API Patterns Skill

• JWT middleware integration
• Error response formats (401, 403)
• OpenAPI security schemas
• CORS configuration

Dashboards Skill

• Role-based widget visibility
• User profile display
• Permission-based data filtering
• Audit trail visualization

Observability Skill

• Auth event logging (login, logout, permission denied)
• Failed login tracking
• Token refresh monitoring
• Security incident alerting

Scripts

Generate JWT Keys

python scripts/generate_jwt_keys.py --algorithm EdDSA

Generates EdDSA or ES256 key pairs for JWT signing.

Validate OAuth 2.1 Configuration

python scripts/validate_oauth_config.py --config oauth.json

Validates OAuth 2.1 compliance (PKCE enabled, exact redirect URIs, etc.).

Examples

Auth.js + Next.js

Complete implementation with OAuth providers, credentials, and session management.

Location: examples/authjs-nextjs/

Keycloak + FastAPI

Self-hosted Keycloak with FastAPI integration via OIDC.

Location: examples/keycloak-fastapi/

Passkeys Demo

Runnable passkeys implementation with @simplewebauthn.

Location: examples/passkeys-demo/

Reference Documentation

• references/oauth21-guide.md - OAuth 2.1 implementation guide
• references/jwt-best-practices.md - JWT generation, validation, storage
• references/passkeys-webauthn.md - Passkeys/WebAuthn implementation
• references/authorization-patterns.md - RBAC, ABAC, ReBAC comparison
• references/password-hashing.md - Argon2id parameters, migration