Implement Token Billing

From http://www.paymentexpress.com/technical_resources/ecommerce_nonhosted/px...

Token Billing allows for regular billing of a cardholder card, under the control of the merchant, without requiring the merchant to either store sensitive card data securely or to obtain credit card details every time a new payment is requested. This functionality is implemented by proving the ability for a merchant to request payment express to capture and store credit card number and expiry date and to link these stored details to a merchant supplied "BillingId". The BillingId is a 32 character field that contains a reference that is unique to the merchant's customer, that will be associated with the credit card information stored securely at Payment Express. This is undertaken during the Setup Phase. For subsequent charges to the card (Rebill Phase), the merchant does not need to supply the card number or expiry date, only the BillingId originally associated during the Setup Phase.