private static Mac createKeyedHmacSha256(byte[] rawKey) {
        var hmac = createHmacSha256();
        try {
            hmac.init(hmacKeyFrom(rawKey));
        } catch (InvalidKeyException e) {
            throw new RuntimeException(e);
        }
        return hmac;
    }
@return a new HKDF instance initially keyed with the given PRK
security-utils/src/main/java/com/yahoo/security/HKDF.java