Two questions about best practices when developing a billing module

[Alex Dunae]

I'm putting together a billing module for EVO Canada (http://www.evocanada.com/) and have a few questions about best practices before submitting.  Any guidance is much appreciated.

1) The gateway returns both an auth code and a transaction ID for purchases, etc...  For voids, updates and refunds the gateway wants the transaction ID passed back as a reference, not the auth code.  It makes sense to me, then, to store the transaction ID in Response#authorization and just store the auth code is a regular param on the Response object.

2) The gateway returns a basic bit of response text and then a code referencing a longer message.  I currently just return the longer message, but in some cases the short message is more descriptive.  For example, the gateway replies with `message=Invalid username&code=300` where code 300 just says 'Rejected by gateway'.  In most other cases the result is more like `message=DECLINED&code=203` and code 203 maps to 'Insufficient funds'.  Should I concatenate the messages together?

Thanks in advance for any suggestions,

Alex