title: Magento - Upload file during registration
body: <p>I want every user, that registers on my Magento instance, to upload a certificate that shows me that he registered a business.</p>
  
  <p>I already added the fields in the template. But how can I fetch the file and save the filename / contents in the customer record?</p>
  
  <p>Is there a way to extend the functionality in the Controllers?</p>