Support transactionId in the webhook notification

[judgej]

This is not supported directly with the gateway API, but could be bolted on through the notify URI. If the notify URI is automatically modified to add the transactionId as a query parameter, then the acceptNotification could read that. Several things to consider:

• It must be optional; some sites may use alternative approaches at the front end. Manipulation of the notify URL may cause problems.
• The nofityUrl is optional; it can be set at the account level and optionally overridden by the merchant site at run-time. Only if overridden does this become possible.
• The notification endpoint is not signed, so anything sent as query parameters could in theory be manipulated en-route. It perhaps needs to be signed, which could make the URL substantially longer. Again, this could be enabled (or disabled) as an option.

Some research to see what other people are doing here:

https://community.developer.authorize.net/t5/Integration-and-Testing/Hosted-Payment-Page-non-iframe-tying-refId-to-transId/td-p/63228