public static byte[] toRawX25519PrivateKeyBytes(XECPrivateKey privateKey) {
        var maybeScalar = privateKey.getScalar();
        if (maybeScalar.isPresent()) {
            return maybeScalar.get();
        }
        throw new IllegalArgumentException("Could not extract scalar representation of X25519 private key. " +
                                           "It might be a hardware-protected private key.");
    }
Returns the bytes representing the BigInteger of the X25519 public key EC point U coordinate
security-utils/src/main/java/com/yahoo/security/KeyUtils.java