This MD5 call has 3 arguments, "MD5", the string, and then the $transaction_key
hash_hmac("md5", $api_login_id . "^" . $fp_sequence . "^" . $fp_timestamp . "^" . $amount . "^", $transaction_key);
How would I reproduce this in Scala? I can't find an MD5 function that takes a "key".