How to embed shopify store in to my website to provide app customisation interface?

[kast]

Essentially I would like to provide UI/Interface like this app:
https://icart.identixweb.com/icart/client/editor.php?scid=MFkweEJ0WExrdTdXZUdpcDl4Y1lJZz09
<iframe src="shopify-url" /> does not work for security reasons.
How does the example above work?

[mkamalkayani]

In the example, the preview is being served from the app's backend. 

"https://icart.identixweb.com/icart/client/preview.php?page_id=3209&shop=popup-store-demo.myshopify.c..."

One possibility is, the app's server makes a request to get the store, modifies it's headers i.e 'X-Frame-DENY' etc and then sends it to the app frontend.