Shopify/active_merchant — pull request #338 by mikel (2012-04-07 12:34:20+00:00)
Title: Add support to PaymentExpress for BillingId as well as DpsBillingId for token

PaymentExpress supports a user specified token as well as DPS auto generated token. This patch upgrades the gateway to allow you to opt in to use the user specified token.

Default behaviour remains the same (using DpsBillingId) so no existing user of ActiveMerchant's PaymentExpress gateway using token based billing will have to change their code.