NeuralTrust | Platform for Agent Security.

AWS WAF cannot call external services. Use Lambda@Edge on viewer request with Include Body.

Coverage

Surface	Monitor	Block	Redact
LLM input	✅	✅	❌
LLM output	❌	❌	❌
Tool-level	➖	➖	➖

Ask — the function returns 403 on block and forwards everything else, so an ask gate is allowed. Write the rule as Block if you need a hard stop. Use it when you serve AI endpoints through CloudFront and want the control alongside AWS WAF. Not when your prompts exceed the viewer-request body limit. Limits. CloudFront truncates the exposed body silently above that limit — the request does not fail, part of the prompt is evaluated and the rest goes through unseen. Measure your prompt sizes before treating this as a control. Lambda@Edge has no environment variables, so the key must come from Secrets Manager or SSM. Input only, no redaction. Full comparison: Coverage.

Node.js Lambda in us-east-1, deploy as Lambda@Edge.
Viewer request + Include Body (body is not exposed otherwise).
No env vars on Lambda@Edge — load the key from Secrets Manager / SSM at cold start, or bake it at deploy.
CloudFront truncates bodies over the viewer-request size limit.

export const handler = async (event) => {
  const request = event.Records[0].cf.request;

  if (request.method === "POST" && request.body?.data) {
    const text = Buffer.from(request.body.data, "base64").toString();
    const result = await fetch("{TRUSTGUARD_URL}/v1/evaluate", {
      method: "POST",
      headers: {
        Authorization: "Bearer <collector-api-key>",
        "Content-Type": "application/json",
      },
      body: JSON.stringify({
        protocol: "llm",
        direction: "input",
        payload: { input: text },
        consumer_id: request.headers["x-user-id"]?.[0]?.value ?? "",
        session_id: request.headers["x-session-id"]?.[0]?.value ?? "",
      }),
    }).then((r) => r.json());

    if (result.status === "block") {
      return { status: "403", statusDescription: "Forbidden", body: "Blocked by TrustGuard" };
    }
    if (result.status === "transform" && result.transformed_payload) {
      request.body.data = Buffer.from(JSON.stringify(result.transformed_payload)).toString("base64");
    }
  }

  return request;
};

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AWS CloudFront

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