Enable check_origin on gateway websocket communication (#5471)

This is a port of the same change in NB2KG (PR 22).

Fixes #5460

Co-authored-by: Dylan <[email protected]>

Co-authored-by: Dylan <[email protected]>

Author: kevin-bates

notebook/gateway/handlers.py

@@ -32,6 +32,9 @@ class WebSocketChannelsHandler(WebSocketHandler, IPythonHandler):
     kernel_id = None
     ping_callback = None
 
+    def check_origin(self, origin=None):
+        return IPythonHandler.check_origin(self, origin)
+
     def set_default_headers(self):
         """Undo the set_default_headers in IPythonHandler which doesn't make sense for websockets"""
         pass