The constraint based product configuration capabilities have improved a lot over the releases of AX2012. One of those capabilities was the ability to use the constraint based configurator over the sales portal. This is something you can find in the later releases. Which is handy it you want to allow internal people or if you have published the sales portal to customers you can get them to configure the order.
Here is a quick overview.
AX2012 R3 CU11.
If you are technical and wanted to understand a little more about the technical interaction of the UI with the web based config and AX then Dennis from the R&D team did a post that you can find here.