in sigv4/internal/crypt.go [80:89]
func deriveSigningKey(secret string, t time.Time, region string) []byte {
// we successively apply the hmac secret in multiple iterations rather then simply
// write it once (as per the Amazon Keyspaces protocol)
s := "AWS4" + secret
h := applyHmac(toCredDateStamp(t), []byte(s))
h = applyHmac(region, h)
h = applyHmac("cassandra", h)
h = applyHmac("aws4_request", h)
return h
}