Shopware Sales Channels - CORS problems with assets on different domains - shopware

Question

Note: After writing the question, someone from our team had an idea that this may be related to the domain of the server which on which Webpack runs when building the assets, and is only coincidentally related to our sales channel domains, which is kind of supported by the observations.
This would mean that while Shopware/Symfony serves the assets, the asset building is where the problem occurs. Therefore I am leaving the original question intact, because the original question still stands.
I have set up several sales channels for two separate brands with two separate domains on my Shopware instance. The setup is similar to the following:
Brand ABC general shop - example.org (uses ABC theme)
Brand ABC US shop - example.org/us (uses ABC theme)
Brand DEF general shop - secondexample.org (uses DEF theme)
Brand DEF US shop - secondexample.org/us (uses DEF theme)
With ABC and DEF theme both inheriting from a base theme
Now, the problem is that I have some icons and assets in my twig files, such as
{% sw_icon 'example-icon' %}
<img src="{{ asset('bundles/defthemeplugin/assets/media/example-media.gif', 'asset') }}">
After setting everything up, I have noticed that the code above returns an absolute URL in the Example domain, e.g. example.org/bundles/defthemeplugin/assets/media/example-media.gif. This results in assets not being downloaded by the browser due to CORS requests being rejected.
Now, interestingly enough, I have found three more clues:
The secondexample.org/us website has the same absolute URLs as the HTML rendered in the secondexample.org sales channel, pointing to the example.org domain
If I change the first sales-channel's URL to thirdexample.org, then the asset URLs on secondexample.org still point to example.org
This is in no way connected to APP_URL in .env, as this is set to a different value that doesn't pop up in asset URLs
After every step/experiment I cleared the cache, rebuilt the JS, etc.
The whole project has a bit complicated architecture, but I believe I can describe it in more detail if need be. I have also not checked what happens on the example.org when it is swapped to some third domain, as currently I am not able to test that scenario.
My question is - where can I find the configuration or logic that decides what domain (or what string) gets put in front of the assets, icons, and all.css or all.js files for a given sales channel domain? Bonus question - how can I influence it so that the right domain is used for these links?
The Shopware version this was tested on is 6.4.10

Answer 1

I think you are right and this happens during the build process.
Checking the theme we are using, I found the variable #{$sw-asset-theme-url} is used:
#font-face {
src: url('#{$sw-asset-theme-url}/bundles/ ....
}
This is put on the fly into var/theme-variables.scss in the ThemeCompiler.
So if you want to use the same theme from different domains, you might need to add the CORS headers.