Merge branch '3.4' into 4.3

* 3.4:
  Adding instructions to prevent CORS errors

Author: javiereguiluz

frontend/encore/dev-server.rst

@@ -29,15 +29,34 @@ This will start a server at ``https://localhost:9000``.
 Hot Module Replacement HMR
 --------------------------
 
-Encore *does* support `HMR`_, but only in some areas. To activate it, pass the ``--hot``
+Encore *does* support `HMR`_ for :doc:`Vue.js </frontend/encore/vuejs>`, but
+does *not* work for styles anywhere at this time. To activate it, pass the ``--hot``
 option:
 
 .. code-block:: terminal
 
     $ ./node_modules/.bin/encore dev-server --hot
 
-HMR currently works for :doc:`Vue.js </frontend/encore/vuejs>`, but does *not* work
-for styles anywhere at this time.
+If you experience issues related to CORS (Cross Origin Resource Sharing), add
+the ``--disable-host-check`` and ``--port`` options to the ``dev-server``
+command in the ``package.json`` file:
+
+.. code-block:: diff
+
+    {
+        ...
+        "scripts": {
+    -        "dev-server": "encore dev-server",
+    +        "dev-server": "encore dev-server --port 8080 --disable-host-check",
+            ...
+        }
+    }
+
+.. caution::
+
+    Beware that `it's not recommended to disable host checking`_ in general, but
+    here it's required to solve the CORS issue.
 
 .. _`webpack-dev-server`: https://webpack.js.org/configuration/dev-server/
 .. _`HMR`: https://webpack.js.org/concepts/hot-module-replacement/
+.. _`it's not recommended to disable host checking`: https://webpack.js.org/configuration/dev-server/#devserverdisablehostcheck