Problems with Freemarker - utils.digest.hmac Hmac SHA256 and base 64 encoding?

The access token expires so we have to hash another challenge each time to get a new token. The Freemarker routine returns base 64 as per the docs so no need to encode it like we do for the php. The php and freemarker agree on the hash, it’s only when we try to pass a byte array to the freemarker (the output from the base 64 decode should be straight binary) The fact I can’t decode and re-encode in Base 64 using Freemarker is somehow related..