@Override
    public byte[] expand(byte[] prk, byte[] info, int nBytesToExpand) {
        return HKDF.ofPseudoRandomKey(prk).expand(nBytesToExpand, info);
    }
KDF implementation using HKDF-SHA256

@author vekterli
security-utils/src/main/java/com/yahoo/security/hpke/HkdfSha256.java