Description
WebEngine's demobrowser uses QNAM for downloading icons propagated by the iconUrlChanged signal. QNAM can't download icons when visiting authenticated pages since the credentials are handled by Chromium. Use Chromium's WebContents::DownloadImage() instead and provide API to use it indirectly via the WebEngine API.
The problem is the same for the Quick API. The Quick Image item doesn't support the authentication and can't download the icon in this case. Provide the icon downloaded by WebContents::DownloadImage() via the Quick API somehow (new quick item for icons, imageprovider, etc)
Moreover, WebEngine's API for icons (favicon manager) should be able to provide the best quality of icons if set. This could be configured via WebEngine Settings (icon download modes).
The QtWebKit's Widget API has a QIcon icon() method that returns the icon for the current page. This API should be added to WebEngine Widgets too.