Add product in magento from an external site.

I currently have a wesite in CakePHP with Custom Product Builder where users can select customize parts of their choice and eventually add this to their cart. We need to integrate Magento shopping cart with Cake PHP. Since it’s a customized product, it would be difficult to add them one by one thru Magento. So what I’d like to do everytime a user submits the customize product is to add this automatically to Magento. I mean not setting/creating the product thru Magento admin but creating the product externally.