Security

This skill is for securing your app's code and data. For regulatory compliance (HIPAA, SOC 2, GDPR), use compliance. For pre-launch readiness checks, use go-live. For environment variable setup during deployment, use deploy. For database-level security (Row Level Security), use database.

Don't Do Yet

• Don't implement OAuth/SSO until you have paying customers who need it. Email + password is fine for launch.
• Don't buy a pentest until you have 1,000+ users or handle sensitive data (health, finance). This checklist is enough for MVP.
• Don't set up a Web Application Firewall (WAF) — your hosting platform (Vercel, Railway) handles this. You don't need Cloudflare yet.
• Don't build your own auth system. Use Supabase Auth, Clerk, or NextAuth. Rolling your own is how breaches happen.

Quick Start

Claude Code:

Run a security audit on my app. Check for:
- API keys or secrets in code (should be in .env)
- Missing auth on protected routes
- SQL injection risks
- XSS vulnerabilities
- Missing rate limiting
Fix anything you find.

Lovable / Replit / Cursor (paste into chat):

Review my app for security issues. Check these common problems:
1. Are any API keys or passwords hardcoded? Move them to environment variables.
2. Can someone access pages without logging in? Add auth checks.
3. Is user input validated before hitting the database?
4. Are passwords hashed (not stored as plain text)?
5. Is rate limiting set up on API endpoints?
Show me what needs fixing and fix it.

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Security Checklist

Security Basics:
- [ ] Authentication required for protected routes
- [ ] Passwords hashed (bcrypt/argon2), never stored plain text
- [ ] API keys in environment variables, not code
- [ ] HTTPS only in production
- [ ] Input validated on server side
- [ ] SQL injection prevented (use parameterized queries)
- [ ] XSS prevented (sanitize user input)
- [ ] CSRF tokens on forms
- [ ] Rate limiting on API endpoints
- [ ] User sessions expire (30min-1hr typical)

See COMMON-VULNS.md for detailed checks.

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Critical: Never Store These in Code

Move to environment variables:

• Database passwords
• API keys (Stripe, SendGrid, etc)
• JWT secrets
• OAuth client secrets
• Encryption keys

Tell AI:

Store API keys in .env file, not in code.
Add .env to .gitignore.
Access via process.env.API_KEY

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Authentication

Use a service. Don't build this yourself.

If you use...	Auth solution
Supabase	Supabase Auth (built in)
Next.js	NextAuth.js or Clerk
Lovable	Supabase Auth (Lovable's default)
Replit	Replit Auth or Supabase

If you must build auth yourself (not recommended), the minimums are:

• Passwords: 8+ chars, hashed with bcrypt (12 rounds), never stored plain text
• Email verification required for signups
• Password reset via email token only
• Sessions expire after 30-60 minutes idle

Tell AI:

Set up authentication using [Supabase Auth / NextAuth / Clerk].
I need: email+password signup, email verification, password reset,
and session timeout after 30 minutes of inactivity.

See SECURITY-PROMPTS.md for implementation details.

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Data Protection

Always encrypt:

• Passwords (hashed, not encrypted)
• Payment info (use Stripe, don't store cards)
• Personal identifiable information (PII)

Never log:

• Passwords (even hashed)
• Credit card numbers
• API keys
• Session tokens

Tell AI:

Never log sensitive data.
Replace passwords/tokens with "[REDACTED]" in logs.

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API Security

Required for all API endpoints:

• Authentication check
• Rate limiting (prevent abuse)
• Input validation
• Error messages don't leak info

Tell AI:

Add to all API routes:
- Require valid auth token
- Rate limit: 100 requests/minute per IP
- Validate all inputs (reject invalid)
- Generic error messages (no stack traces to users)

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Common Vulnerabilities

Most common in AI-built apps:

1. Exposed API keys - In code instead of .env
2. No rate limiting - APIs can be spammed
3. Missing auth checks - Routes accessible without login
4. SQL injection - Raw SQL with user input
5. XSS attacks - Unescaped user content displayed

See COMMON-VULNS.md for how to check.

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Security Prompts for AI

Adding authentication:

Add authentication to this route.
Require valid JWT token.
Return 401 if missing/invalid.
Don't expose error details.

Rate limiting:

Add rate limiting:
- 100 requests/minute per IP
- Return 429 "Too many requests" if exceeded
- Use sliding window, not fixed

Input validation:

Validate all user inputs:
- Email: valid format
- Password: 8+ chars, 1 number, 1 symbol
- Username: alphanumeric only, 3-20 chars
Reject invalid input with clear error message

See SECURITY-PROMPTS.md for more.

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Pre-Launch Security Review

Before deploying:

Production Security:
- [ ] All secrets in environment variables
- [ ] HTTPS enforced (no HTTP)
- [ ] Database backups configured
- [ ] Rate limiting on all APIs
- [ ] Error pages don't show stack traces
- [ ] Admin routes protected
- [ ] File uploads validated (type, size)
- [ ] CORS configured (not wildcard "*")

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When to Get Security Audit

Signs you need expert review:

• Handling payments directly (not Stripe)
• Storing health/financial data
• Multi-tenant with data isolation
• Over 1,000 users
• Processing sensitive PII

For most MVPs: Following this checklist is sufficient.

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Common Founder Mistakes

Mistake	Fix
API keys in code	Move to .env
No rate limiting	Add to all endpoints
Plain text passwords	Use bcrypt
HTTP in production	Force HTTPS
Accepting all CORS	Whitelist domains
No input validation	Validate server-side
Detailed error messages	Generic messages only

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Quick Wins

Easy security improvements:

1. Add Helmet.js (Node) - Sets security headers
2. Use HTTPS everywhere - Force in production
3. Add rate limiting - Prevents abuse
4. Environment variables - Keep secrets safe
5. Update dependencies - Fix known vulnerabilities

Tell AI:

Add helmet.js for security headers.
Configure for production (HTTPS, CSP, XSS protection).

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Testing Security

Quick checks:

Exposed secrets:

grep -r "api_key" src/
grep -r "password" src/
# Should only find references to env vars

No auth bypass:

• Try accessing protected routes without login
• Should redirect to login or return 401

Rate limiting works:

• Hit API endpoint 100 times quickly
• Should get 429 error

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Success Looks Like

✅ No secrets in code (all in .env) ✅ Can't access protected routes without auth ✅ Passwords hashed, never stored plain text ✅ Rate limiting prevents abuse ✅ HTTPS enforced in production ✅ Input validated on server side

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Related Skills

• compliance — Regulatory requirements (HIPAA, SOC 2, GDPR, CCPA)
• go-live — Pre-launch readiness checks (security is one part of this)
• deploy — Hosting and environment variable setup
• database — Row Level Security, data access policies
• payments — Stripe security and PCI compliance