The output of Document#getExternalURL() in the PDF cover doesn't match the URL used to access XWiki

Follow these steps to reproduce:

• configure XWiki to use the Chrome Docker container for generating PDFs (or a remote Chrome instance)
• create a custom PDF template, and modify the cover field to also print:

  $tdoc.externalURL
  

• register the created PDF template in the PDF export administration section
• export a page to PDF using the custom PDF template
• check the cover page

Expected: the external URL printed in the cover page matches the URL used to access XWiki (same protocol, same domain, same port).
Actual: the external URL printed on the cover page is the URL used by the headless Chrome instance to access XWiki, which is different from the URL used by the user to access XWiki.