For Authorize.net the `authorization` is the transaction_id - their own internal, unique id.  The `authorization_code` is issued by some banking institution. https://support.authorize.net/authkb/index?page=content&id=A469&actp=LIST

If the authorization_code is something not used by other gateways, perhaps Authorize.net should have it's own (subclass) Response object ?  Sorry, I did not understand your comment about leaving it in the params.