Unable to detect if a request is an AJAX request

I'm currently using Vaadin 8 and trying to set up a new authentication process that needs to comply with (when the user is not authenticated):

AJAX request: 401 Unauthorized
Other requests: 302 Redirect

The framework already tries to inspect the request and determine if it is an AJAX one by one of the criteria below:
There is a header X-Requested-With with XMLHttpRequest
There is either a header or a parameter with is_ajax_request

Vaadin only set the following headers:
Accept
Accept-Language
Accept-Encoding
Origin
User-Agent
Connection
Content-Type
Cookie
Content-Length
Referer
Host

And there is also no is_ajax_request parameter.

So, the only way I could achieve the desired behaviour was either using the deprecated com.vaadin.server.ServletPortletHelper#isUIDLRequest or doing something as ugly as context?.fullRequestURL?.contains("/UIDL") ?: false.

Can Vaadin implement a proper way of detecting if a request is an AJAX one or not?

Thanks in Advance.

Information:

• Vaadin Framework version (e.g. 8.6.0)
• Browser version: Chrome latest
• Web container name and version: Wildlfy

Start by reviewing the deprecated com.vaadin.server.ServletPortletHelper#isUIDLRequest method and the request handling associated with the /UIDL endpoint. Determine how Vaadin can expose a supported AJAX-request check, then verify that unauthenticated AJAX and other requests can be distinguished for the requested response behavior.