How to integrate third party payment gateway with B2B storefornt via SOAP or XML API

I have a hybris B2B storefront on 5.2 version. I want to integrate third party payment gateway provided by customer with my B2B store. This third party payment gateway support XML and SOAP API. Please provide me the approach/steps or some trials etc by which I can integrate the payment gateway with my B2B storefront. I think CIS support restfull not SOAP API, please correct me if I am wrong.