Apple tells developers,
"You can find a list of payment providers who support Apple Pay with their SDKs
on developer.apple.com/apple-pay/. Using one of these SDKs is highly recommended."
These six are:
Authorize.Net, Chase Paymentech, CyberSource, First Data, Stripe and TSYS.
As notable as inclusion are those who are absent.Source: http://www.pymnts.com/news/2014/apple-pay-recommends-six-processors-and-paypals-not-one-of-them/
Related: https://news.ycombinator.com/item?id=8330629