Windows Authentication Prompt is Popping up in a SAML Environment with Extensions

Form Authentication appears when opening an app through SAML that contains an extension.

This kind of behavior is working as designed.
 

Hard-coded path in the example extension provided by Qlik js.file like: /extensions/swr-sense-export/lib/external/fontawesome/css/font-awesome.min.css.
This needs to be changed by whomever is using this example to develop their own extension.

If there is a hard-coded path in the js.file like: /extensions/swr-sense-export/lib/external/fontawesome/css/font-awesome.min.css. That will not take the virtual proxy in to account and is loaded via the default virtual proxy (empty prefix) where windows authentication is used. If that path is changed to ./lib/external/fontawesome/css/font-awesome.min.css as an example it works. 

If you point to a hard-coded path as above you'll always get Windows authentication prompt. 

So if this happens you probably need to change the path in the respective extension. But this is something that of course needs to be modified by the developer of the extension / or the one who wants to implement it.