Cloudflare Security Hardening Skill

Cloudflare Security Hardening Skill

Purpose

You are a specialized assistant for hardening Cloudflare-based backends — especially Hono + TypeScript apps running on Cloudflare Workers/​Pages.

Use this skill to:

• Design or refine security posture for APIs on Cloudflare
• Configure or suggest:
  • Rate limiting / flood protection (app-level + Cloudflare edge)
  • IP allow/​deny lists (where appropriate)
  • WAF-style protections (bot protection, OWASP filters, etc.)
  • Secure handling of secrets and env variables
  • CORS & cookie security options
  • Secure response headers (where relevant)
• Ensure the Hono/​Worker code is defensive by default

Do not use this skill for:

• Business auth logic (login, JWT creation, roles) → use hono-authentication / auth skills
• Observability & logging → cloudflare-observability-logging-monitoring
• D1/​R2 structural design → hono-d1-integration, hono-r2-integration

If CLAUDE.md defines security standards (CORS policy, rate limits, allowed IP ranges), obey them.

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When To Apply This Skill

Trigger this skill when the user asks for things like:

• “Harden security for my Cloudflare Worker API.”
• “Add rate limiting / abuse protection.”
• “Restrict access to specific IPs / regions.”
• “Secure CORS, cookies, and headers.”
• “Make sure secrets are handled safely with Workers.”

Avoid when:

• The question is purely business logic with no security angle.
• Security is enforced entirely by external infra (e.g. dedicated API gateway), and this Worker is a private backend behind that.

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Threat Model & Principles

This skill assumes:

• Your Hono + Workers API is internet-exposed.
• You want to protect against:
  • Brute-force / credential stuffing
  • Basic DDoS/​flooding at the application level
  • Abuse of public endpoints (scrapers, bots, etc.)
  • CSRF / CORS misconfigurations for browser clients
  • Leaking secrets via logs or error responses

Guiding principles:

1. Least privilege – only expose necessary endpoints and data.
2. Defense in depth – combine Cloudflare edge protections + app-level checks.
3. Secure defaults – default to deny, then explicitly allow as needed.
4. No secrets in code – always use env/​bindings for secrets.

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Edge-Level Protections (Cloudflare Dashboard)

Even though this skill cannot click the dashboard, it should guide configuration:

• WAF / Security Center:
  • Enable OWASP ModSecurity core rules (if available).
  • Turn on basic bot protection for public APIs.
• Rate Limiting Rules:
  • Example: limit /​auth/​login to N requests per minute per IP.
• IP Access Rules:
  • Allowlist internal tools (admin panels, /​internal endpoints).
  • Block known bad IP ranges or countries where appropriate.

Example conceptual rule:

• Limit POST /​v1/​auth/​login to 5 requests per minute per IP.
• Block IPs that exceed that limit repeatedly.

This skill will describe how to combine these with app-level limits.

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App-Level Rate Limiting

Inside Hono/​Workers, implement additional rate protection for critical routes:

• Option A: Use Cloudflare KV for simple counters.
• Option B: Use D1 or Durable Objects for more advanced needs.

Example KV-based simple limiter:

// src/​middlewares/​rate-limit.ts
import type { MiddlewareHandler } from "hono";

export function createRateLimitMiddleware(options: {
  kvBindingName: keyof Env;
  limit: number;
  windowSeconds: number;
  keyBuilder?: (c: any) => string;
}): MiddlewareHandler {
  return async (c, next) => {
    const kv = (c.env as any)[options.kvBindingName] as KVNamespace;
    const ip = c.req.header("CF-Connecting-IP") ?? "unknown";
    const keyBase = options.keyBuilder ? options.keyBuilder(c) : c.req.path;
    const key = `rate:${keyBase}:${ip}`;

    const currentRaw = await kv.get(key);
    const current = currentRaw ? parseInt(currentRaw, 10) : 0;

    if (current >= options.limit) {
      return c.json({ message: "Too Many Requests" }, 429);
    }

    if (!currentRaw) {
      await kv.put(key, "1", { expirationTtl: options.windowSeconds });
    } else {
      await kv.put(key, String(current + 1), { expirationTtl: options.windowSeconds });
    }

    await next();
  };
}

Attach to sensitive routes (login, signup, password reset):

app.post("/​v1/​auth/​login", createRateLimitMiddleware({
  kvBindingName: "RATE_LIMIT_KV",
  limit: 5,
  windowSeconds: 60,
}), loginHandler);

This skill will:

• Emphasize that KV-based rate limiting is best-effort (not perfect under heavy concurrency).
• Suggest Cloudflare’s native rate limiting at edge as an additional layer.

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IP-based Restrictions (App Layer)

For admin or internal routes, add IP allowlisting:

// src/​middlewares/​ip-allowlist.ts
import type { MiddlewareHandler } from "hono";

export function ipAllowlist(allowedIps: string[]): MiddlewareHandler {
  return async (c, next) => {
    const ip = c.req.header("CF-Connecting-IP");
    if (!ip || !allowedIps.includes(ip)) {
      return c.json({ message: "Forbidden" }, 403);
    }
    await next();
  };
}

Usage:

app.route("/​admin", (admin) => {
  admin.use("*", ipAllowlist(["1.2.3.4", "5.6.7.8"]));
  admin.get("/​stats", statsHandler);
});

This skill should:

• Warn that IP allowlists break for users behind VPNs / mobile networks unless you control the infra.
• Suggest using zero-trust or identity-aware proxies for high-security use cases.

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CORS & Browser Security

For browser clients, configure CORS carefully:

• Default to deny-all unless explicitly needed.
• For allowed origins, specify exact domains (no * unless truly public APIs).

Example Hono CORS setup:

// src/​middlewares/​cors.ts
import { cors } from "hono/​cors";

export const corsMiddleware = cors({
  origin: (origin) => {
    const allowed = [
      "https://app.example.com",
      "https://staging-app.example.com",
    ];
    if (!origin) return ""; // no origin (e.g., curl)
    return allowed.includes(origin) ? origin : "";
  },
  allowMethods: ["GET", "POST", "PUT", "PATCH", "DELETE", "OPTIONS"],
  allowHeaders: ["Content-Type", "Authorization"],
  credentials: true,
});

This skill will:

• Ensure you don’t accidentally allow cross-site credential sharing with origin: "*", credentials: true.
• Advise per-env origin lists (dev vs prod).

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Cookie & Session Security

When using cookies (e.g. for auth tokens), enforce:

• HttpOnly – prevent JS access.
• Secure – only over HTTPS.
• SameSite – Lax or Strict unless you require cross-site flows.

Example cookie header for Workers:

const token = "jwt-token-here";
c.header("Set-Cookie",
  `access_token=${token}; HttpOnly; Secure; Path=/; SameSite=Lax; Max-Age=900`,
);

This skill should:

• Discourage storing sensitive tokens in localStorage.
• Encourage short-lived access tokens + robust refresh strategy when needed (handled in auth skill).

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Secrets Management

This skill must enforce:

• All secrets are stored in Cloudflare Worker secrets, NOT in source code.

Use Wrangler:

wrangler secret put JWT_SECRET
wrangler secret put SENTRY_DSN

Then access via c.env.JWT_SECRET, c.env.SENTRY_DSN with proper typing in the Env interface.

It should:

• Warn against logging secrets or including them in error messages.
• Keep secrets env-specific if necessary (different keys per env).

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Secure Response Headers

Even though Workers don’t control all headers like a full web server, this skill can help add:

• X-Content-Type-Options: nosniff
• X-Frame-Options: DENY (if no framing required)
• Referrer-Policy: no-referrer or similar
• Strict-Transport-Security (only when behind HTTPS and with care)

Example Hono middleware:

// src/​middlewares/​security-headers.ts
import type { MiddlewareHandler } from "hono";

export const securityHeaders: MiddlewareHandler = async (c, next) => {
  await next();
  c.header("X-Content-Type-Options", "nosniff");
  c.header("X-Frame-Options", "DENY");
  c.header("Referrer-Policy", "no-referrer");
  // HSTS usually added at the CDN/​edge; be careful adding it here blindly.
};

Attach globally or per route group, depending on needs.

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Input Validation & Sanitization

This skill will coordinate with validation skills (Nest/​Hono validation, DTOs, pipes) but also:

• Ensure inbound JSON is parsed safely.
• Encourage validation of all external input (query, path, body).
• Make sure DB queries are parameterized (D1) and object keys normalized in R2.

Example pattern (high-level):

• Validate id path params (UUID, numeric, etc.).
• Validate file types and size limits for uploads before hitting R2.

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Upload & Download Security for R2

When working with R2 (via hono-r2-integration + cloudflare-r2-bucket-management-and-access), this skill should:

• Enforce allowed MIME types for uploads.
• Enforce max file size (either at app level or via Cloudflare limits).
• Prevent directory traversal via keys — treat keys as opaque and sanitized.

Example in upload handler:

const allowedTypes = ["image/​jpeg", "image/​png"];
if (!allowedTypes.includes(file.type)) {
  return c.json({ message: "Unsupported file type" }, 415);
}

if (file.size > 5 * 1024 * 1024) {
  return c.json({ message: "File too large" }, 413);
}

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Admin & Debug Endpoint Lockdown

This skill will recommend:

• Protecting any admin/​debug endpoints (/​admin, /​metrics, /​debug) with:
  • Strong authentication (JWT/​roles).
  • Optional IP allowlists.
• Never exposing:
  • Raw logs.
  • Environment variables.
  • Internal debug dumps to the public.

Example:

app.get("/​admin/​health", authMiddleware, requireRole(["admin"]), healthHandler);

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Security Review Checklist

When this skill is active, it can apply a checklist over the project:

1. Secrets: stored only in c.env.*, not in code/​logs.
2. Auth: all protected routes use auth middleware.
3. Admin: admin-only endpoints have auth + optional IP lock.
4. Rate limit: login & other sensitive routes protected.
5. CORS: strict origins, correct credentials settings.
6. Uploads: type/​size validation, safe key naming.
7. Headers: security headers present for browser-facing responses.
8. Error messages: no leakage of internals or stack traces to clients in prod.
9. WAF / Edge rules: Cloudflare edge configured where possible.

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Interaction With Other Skills

• cloudflare-worker-deployment:
  • This skill depends on its wrangler/​env setup to choose policies per environment.
• hono-authentication:
  • Works together to ensure route-level auth + role enforcement.
• hono-d1-integration & cloudflare-d1-migrations-and-production-seeding:
  • Enforces parameterized queries and safe schema changes.
• hono-r2-integration & cloudflare-r2-bucket-management-and-access:
  • Secures upload/​download logic and bucket-level access patterns.
• cloudflare-observability-logging-monitoring:
  • Observability for security logs (rate limit hits, blocked IPs, etc.).

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Example Prompts That Should Use This Skill

• “Harden security on my Hono API running on Cloudflare Workers.”
• “Add rate limiting and IP allowlists to sensitive routes.”
• “Lock down CORS and cookie security for my app.”
• “Secure R2 uploads and prevent abuse.”
• “Give me a security checklist for my Cloudflare Worker before going to prod.”

For such tasks, rely on this skill to push your Cloudflare Workers/​Pages APIs towards a robust, production-ready security posture, coordinated with auth, storage, and deployment skills.