Shopify/active_merchant — pull request #1290 by duff (2014-07-04 18:36:33+00:00)
Title: First Data E4: Add ability to verify a card

First Data E4 has support for $0 authorizations so we don't need to void
it. It's a "Pre-Authorization Only" transaction rather than a standard
authorization which is a "Pre-Authorization" transaction.

Docs for it:
https://firstdata.zendesk.com/entries/407571-First-Data-Global-Gateway-e4-Web-Service-API-Reference-Guide