Zero-Trust API Security Gate & Fail-Closed Checklist

Target Audience

Designed for Fractional CTOs, Senior Technical Architects, and Engineering Directors auditing high-throughput API gateways and edge execution boundaries. SazM is an AI-Native Software Delivery Platform operated by a Principal Engineer. AI executes software delivery workflows, while senior engineering judgment provides architecture validation, quality assurance, and final approval.

Problem Statement

Public API gateways and edge Workers are subject to continuous automated exploitation attacks, including timestamp replay attempts, credential stuffing, and rate-limit bypasses. Ad-hoc security implementations leave critical vulnerabilities exposed. This checklist provides a production-grade Zero-Trust API Security Gate framework to guarantee fail-closed security at the network edge.

When to Use

Use this checklist prior to launching public API endpoints, during edge Worker security reviews, or when hardening multi-tenant microservices against automated bot traffic.

Step-by-Step Guide

Step 1: Request Authentication & Replay Defense

• Enforce HMAC-SHA256 cryptographic signature validation on all incoming payload bodies.
• Require timestamp header validation within a strict 300-second drift tolerance window to prevent replay attacks.
• Utilize WebCrypto API bindings inside Cloudflare Workers for sub-millisecond cryptographic signature verification.

Step 2: Fail-Closed Rate Limiting & Gateway Boundaries

• Implement sliding-window rate limiters at the edge boundary.
• Configure rate limiters to fail-closed on KV/Durable Object storage exceptions.
• Enforce strict JSON schema validation prior to un-marshalling request parameters into internal application state.

Step 3: Key Management & Audit Trail Verification

• Implement dual-key secret rotation allowing zero-downtime key rollovers.
• Persist structured audit logs containing hashed request fingerprints and client IPs in outbox queues.
• Verify 100% CI pipeline test coverage for security gate middleware prior to production deployment.

Production Validation Examples

// HMAC-SHA256 WebCrypto Signature Verification Example
export async function verifySignature(payload: string, signature: string, secret: string): Promise<boolean> {
  const encoder = new TextEncoder();
  const key = await crypto.subtle.importKey(
    'raw',
    encoder.encode(secret),
    { name: 'HMAC', hash: 'SHA-256' },
    false,
    ['verify']
  );
  const sigBuf = hexToBuffer(signature);
  return crypto.subtle.verify('HMAC', key, sigBuf, encoder.encode(payload));
}

Related Delivery Evidence

• Legacy PHP to Cloudflare Edge Modernization — 14-day migration featuring fail-closed edge rate limiting.
• SazM Platform Architecture Case Study — Execution Gateway signature verification implementation.

Checklist Items

• HMAC-SHA256 request signatures verified at the network boundary using WebCrypto.
• Timestamp headers validated within a 300-second maximum drift window.
• Edge rate limiters configured to fail-closed under KV/DO storage failures.
• JSON payload schemas strictly validated before un-marshalling.
• Dual-key rotation active with zero-downtime key rollovers.
• Audit trail logs persist hashed fingerprints without exposing sensitive PII.
• Automated security regression test suite passes in CI before release.
• Server version and platform infrastructure headers stripped from all responses.