API Security Hardening Skill for Claude
REST API security hardening with authentication, rate limiting, input validation, security headers. Use for production APIs, security audits, defense-in-depth, or encountering vulnerabilities, injection attacks, CORS issues.
Install
one command, takes just this skill from the repositorynpx skills add https://github.com/secondsky/claude-skills --skill api-security-hardeningThe instruction itself
7 sections, as written by the authorAPI Security Hardening
Protect REST APIs against common vulnerabilities with multiple security layers.
Security Middleware Stack (Express)
const helmet = require('helmet');
const rateLimit = require('express-rate-limit');
const mongoSanitize = require('express-mongo-sanitize');
app.use(helmet());
app.use(mongoSanitize());
// For input sanitization, see the `xss-prevention` skill — do NOT use the
// deprecated `xss-clean` package (unmaintained since 2018; its own README
// recommends migrating off it).
app.use('/api/', rateLimit({
windowMs: 15 * 60 * 1000,
max: 100
}));
app.use('/api/auth/', rateLimit({
windowMs: 15 * 60 * 1000,
max: 5
}));
Input Validation
const { body, validationResult } = require('express-validator');
const escapeHtml = require('escape-html');
app.post('/users',
body('email').isEmail().normalizeEmail(),
body('password').isLength({ min: 8 }).matches(/[A-Z]/).matches(/[0-9]/),
// express-validator v7+ removed the built-in .escape() sanitizer; use a
// customSanitizer backed by `escape-html` to HTML-escape the value.
body('name').trim().isLength({ max: 100 }).customSanitizer(v => escapeHtml(v)),
(req, res) => {
const errors = validationResult(req);
if (!errors.isEmpty()) {
return res.status(400).json({ errors: errors.array() });
}
// Process request
}
);
Security Headers
app.use((req, res, next) => {
res.setHeader('Content-Security-Policy', "default-src 'self'");
res.setHeader('X-Frame-Options', 'DENY');
res.setHeader('X-Content-Type-Options', 'nosniff');
res.setHeader('Strict-Transport-Security', 'max-age=31536000; includeSubDomains');
res.setHeader('X-XSS-Protection', '1; mode=block');
next();
});
Security Checklist
- [ ] HTTPS everywhere
- [ ] Authentication on all protected routes
- [ ] Input validation and sanitization
- [ ] Rate limiting enabled
- [ ] Security headers configured
- [ ] CORS restricted to allowed origins
- [ ] No stack traces in production errors
- [ ] Audit logging enabled
- [ ] Dependencies regularly updated
Additional Implementations
See references/python-nginx.md for:
- Python FastAPI security middleware
- Pydantic input validation with password rules
- Nginx SSL/TLS and security headers configuration
- HTTP Parameter Pollution prevention
Never Do
- Trust user input without validation
- Return detailed errors in production
- Store secrets in code
- Use GET for state-changing operations
- Disable security for convenience
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How to use it
Take secondsky/api-security-hardening from the repository into ~/.claude/skills for personal
use, or into .claude/skills inside a project.
The agent identifies a skill by the name field in its header. Two skills with the
same name cannot sit side by side — one of them will be ignored.