Is there an API to work with CartaSì, in order to make a Magento module to work with CartaSi?

Question

I need to somehow develop and install CartaSi module for payment, integrated with Magento, so a module that collaborates with CartaSi. Any suggestions on how to do this? I have found only couple of expensive Modules on the internet: https://www.magentocommerce.com/magento-connect/payment-module-x-pay-cartasi.html and https://www.magentocommerce.com/magento-connect/modulo-di-pagamento-modulo-key-client-cartasi.html And those are probably good, but we need to be able to modify and prefereably, develop modules for CartaSi on my own.