in src/main/scala/com/gu/hmac/HMACHeaders.scala [103:108]
def validateHMACHeadersWithSecret(secretKey: String, dateHeader: String, authorizationHeader: String, uri: URI): Boolean = {
val hmacDate = HMACDate.get(dateHeader)
val hmacToken = HMACToken.get(authorizationHeader)
isDateValid(hmacDate) && isHMACValid(secretKey, hmacDate, uri, hmacToken)
}