verifySignature(publicKey, payload, signature, timestamp) {
    let timestampPayload = Buffer.isBuffer(payload) ? payload.toString() : payload;
    timestampPayload = timestamp + timestampPayload;
    const decodedSignature = Signature.fromBase64(signature);

    return Ecdsa.verify(timestampPayload, decodedSignature, publicKey);
  }
Verify signed event webhook requests.

@param {PublicKey} publicKey elliptic curve public key
@param {string|Buffer} payload event payload in the request body
@param {string} signature value obtained from the 'X-Twilio-Email-Event-Webhook-Signature' header
@param {string} timestamp value obtained from the 'X-Twilio-Email-Event-Webhook-Timestamp' header
@return {Boolean} true or false if signature is valid