Security Patterns

Apply these security practices when writing or reviewing code in auth, middleware, and API layers.

Input Validation

• Always validate at system boundaries (API endpoints, form handlers, message consumers)
• Never trust client-side validation alone
• Use allowlists over denylists for input filtering
• Validate types, lengths, ranges, and formats
• Sanitize HTML output to prevent XSS (use framework auto-escaping)

SQL Injection Prevention

• Always use parameterized queries or ORM methods
• Never construct SQL with string concatenation or f-strings
• Django: use QuerySet methods, Q objects, or params argument for raw SQL
• Node.js: use query builders (Knex) or ORM (Prisma, TypeORM) -- never template literals in SQL

# WRONG
User.objects.raw(f"SELECT * FROM users WHERE email = '{email}'")

# CORRECT
User.objects.raw("SELECT * FROM users WHERE email = %s", [email])
User.objects.filter(email=email)

Authentication

• Hash passwords with bcrypt, argon2, or scrypt (never MD5/SHA alone)
• Enforce minimum password complexity at registration
• Rate-limit login attempts (exponential backoff or account lockout)
• Use constant-time comparison for tokens and secrets
• Invalidate sessions on password change

JWT / Token Security

• Set short expiration times (15min for access tokens, days for refresh)
• Store refresh tokens server-side (database or Redis)
• Never store sensitive data in JWT payload (it's base64, not encrypted)
• Validate iss, aud, and exp claims on every request
• Use RS256 or ES256 over HS256 for multi-service architectures

CSRF Protection

• Enable framework CSRF middleware (Django: CsrfViewMiddleware)
• Use SameSite=Lax or Strict on session cookies
• For SPAs: use token-based auth or double-submit cookies
• Never disable CSRF protection for convenience

Authorization

• Check permissions on every request, not just in UI
• Use role-based or attribute-based access control
• Verify object ownership: if obj.owner != request.user: return 403
• Log authorization failures for monitoring

Secrets Management

• Never hardcode secrets, API keys, or passwords in code
• Use environment variables or secret managers (AWS Secrets Manager, Vault)
• Add .env and credential files to .gitignore
• Rotate secrets on schedule and after any suspected breach

HTTP Security Headers

Ensure these headers are set in production:

• Strict-Transport-Security: max-age=31536000; includeSubDomains
• Content-Security-Policy: default-src 'self'
• X-Content-Type-Options: nosniff
• X-Frame-Options: DENY
• Referrer-Policy: strict-origin-when-cross-origin

Logging

• Log authentication events (login, logout, failed attempts)
• Log authorization failures
• Never log passwords, tokens, API keys, or PII
• Include request IDs for traceability