Authorize.Net (https://www.authorize.net), a service of Lightbridge, is the preferred global payment-processing service for e-commerce, enabling merchants to process secure transactions in real time, 24 hours a day. Authorize.Net Payment Solutions process credit cards and electronic checks.
r3 has integrated with Authorize.Net API via Advanced Integration Method (AIM), that uses secure sockets layer (SSL) digital certificate technology to connect securely and directly to the Payment Gateway - achieving the highest security for the Internet connection between a merchant and the gateway.
Some of the useful links are listed below:
Find a Authorize.Net Reseller: https://www.authorizenet.com/reseller/directory.php
Signup for Authorize.Net Merchant Account: https://www.authorizenet.com/solutions/gettingstarted.php
Login to Authorize.Net Merchant Account: https://secure.authorize.net/
Support Center: https://www.authorizenet.com/support/