docs: @RenderMapping
      public ModelAndView displaySkinCssHeader(
              RenderRequest request, RenderResponse response, Model model) throws IOException {
  
          // NOTE:  RENDER_HEADERS phase may be called before or at the same time as the
          // RENDER_MARKUP. The spec is
          // silent on this issue and uPortal does not guarantee order or timing of render execution,
          // but does
          // guarantee order of render output processing (output of RENDER_HEADERS phase is included
          // before
          // RENDER_MARKUP phase).  uPortal inserts the HTML markup returned from RENDER_HEADERS
          // execution into the HEAD
          // section of the page.
  
          if (PortletRequest.RENDER_HEADERS.equals(
                  request.getAttribute(PortletRequest.RENDER_PART))) {
  
              PortletPreferences prefs = request.getPreferences();
              Boolean enabled =
                      Boolean.valueOf(
                              prefs.getValue(DynamicRespondrSkinConstants.PREF_DYNAMIC, "false"));
              String skinName =
                      prefs.getValue(
                              DynamicRespondrSkinConstants.PREF_SKIN_NAME,
                              DynamicRespondrSkinConstants.DEFAULT_SKIN_NAME);
              String cssUrl =
                      enabled
                              ? calculateDynamicSkinUrlPathToUse(request, skinName)
                              : calculateDefaultSkinCssLocationInWebapp(skinName);
              model.addAttribute(
                      DynamicRespondrSkinConstants.SKIN_CSS_URL_MODEL_ATTRIBUTE_NAME, cssUrl);
              return new ModelAndView("jsp/DynamicRespondrSkin/skinHeader");
          } else {
              // We need to know if this user can CONFIG this skin
              boolean canAccessSkinConfig = false; // Default
              final HttpServletRequest httpr = portalRequestUtils.getCurrentPortalRequest();
              final IPerson user = personManager.getPerson(httpr);
              final IAuthorizationPrincipal principal =
                      AuthorizationPrincipalHelper.principalFromUser(user);
              final IPortletWindowId portletWindowId =
                      portletWindowRegistry.getPortletWindowId(httpr, request.getWindowID());
              final IPortletWindow portletWindow =
                      portletWindowRegistry.getPortletWindow(httpr, portletWindowId);
              final IPortletEntity portletEntity = portletWindow.getPortletEntity();
              if (principal.canConfigure(portletEntity.getPortletDefinitionId().toString())) {
                  canAccessSkinConfig = true;
              }
              // RENDER_MARKUP
              return new ModelAndView(
                      "jsp/DynamicRespondrSkin/skinBody",
                      DynamicRespondrSkinConstants.CAN_ACCESS_SKIN_CONFIG_MODEL_NAME,
                      canAccessSkinConfig);
          }
      }