[WebUI] Only accept application/json content-type requests

- Protects against CSRF (Cross-site request forgery)

deluge/ui/web/json_api.py

@@ -262,6 +262,10 @@ class JSON(resource.Resource, component.Component):
         Handler to take the json data as a string and pass it on to the
         _handle_request method for further processing.
         """
+        if request.getHeader('content-type') != 'application/json':
+            message = 'Invalid JSON request content-type: %s' % request.getHeader('content-type')
+            raise JSONException(message)
+
         log.debug("json-request: %s", request.json)
         response = {"result": None, "error": None, "id": None}
         response["id"], d, response["error"] = self._handle_request(request)