ParadoxLabs Authorize.Net CIM extensions for Magento 1 and Magento 2 are reliable alternatives to Direct Post and are not impacted by the recently announced MD5 Hash changes.

Magento 2

When you get an extension from ParadoxLabs, you join an international community of thousands of customers who use our services to support over $3 billion in annual transactions. We build top-notch extensions you can extend and modify as you please. If you buy a license, it's yours—plus a year of support, and free updates for the life of the extension.