in src/main/scala/com/gu/googleamp/AmpFlusher.scala [57:63]
private def makeRequestUrl(contentId: String, timestamp: Long): String = {
val cacheUpdateRequestURL =
s"/update-cache/c/s/amp.theguardian.com/${contentId}?amp_action=flush&_ts=${timestamp}"
val signature =
computeSignature(cacheUpdateRequestURL.getBytes, getPrivateKey())
s"https://amp-theguardian-com.cdn.ampproject.org${cacheUpdateRequestURL}&_url_signature=${signatureAsWebSafeString(signature)}"
}