Merge branch '3.4' into 4.2

* 3.4:
  update documentation to add hattip to new crossorigin configuration param

Author: javiereguiluz

frontend/encore/cdn.rst

@@ -38,3 +38,10 @@ You *do* need to make sure that the ``script`` and ``link`` tags you include on
 pages also use the CDN. Fortunately, the
 :ref:`entrypoints.json <encore-entrypointsjson-simple-description>` paths are updated
 to include the full URL to the CDN.
+
+If you are using ``Encore.enableIntegrityHashes()`` and your CDN and your domain
+are not the `same-origin`_, you may need to set the ``crossorigin`` option in
+your webpack_encore.yaml configuration to ``anonymous`` or ``use-credentials``
+to overcome CORS errors.
+
+.. _`same-origin`: https://en.wikipedia.org/wiki/Same-origin_policy