Force authentication when the download fails in an anonymous session

If the anonymous user is enabled and one follows a link to download a file without being authenticated, the download will fail and redirect to the error page with a "No document found" message.

This corresponds to the behavior written in DownloadServiceImpl#handleDownload

            DocumentModel doc = getDownloadDocument(downloadBlobInfo.repository, downloadBlobInfo.docId);
            if (doc == null) {
                resp.sendError(HttpServletResponse.SC_NOT_FOUND, "No document found");
                return;
            }

We need to find a mechanism to force the authentication.