署名シークレットのローテーション

import crypto from "crypto";

// secret is the signing secret currently configured on your receiver.
function isAuthenticWebhook(rawBody, headers, secret) {
  const expected = crypto
    .createHmac("sha256", secret)
    .update(rawBody) // the raw, unparsed request body
    .digest("hex");

  const headerValue = headers["x-authorization-content-sha256-v2"] || "";

  // Accept if ANY v1= signature in the header matches our computed HMAC.
  return headerValue
    .split(",")
    .map((part) => part.trim())
    .filter((part) => part.startsWith("v1="))
    .map((part) => part.slice("v1=".length))
    .some((sig) => {
      const sigBuf = Buffer.from(sig);
      const expectedBuf = Buffer.from(expected);
      // timingSafeEqual throws on length mismatch — treat as not authentic.
      return (
        sigBuf.length === expectedBuf.length &&
        crypto.timingSafeEqual(sigBuf, expectedBuf)
      );
    });
}