I have read several posts related to this, but I have not found one (yet) with a specific answer that fits our scenario. I am using a secured service that sits on an internal server. I can add the feature service, but editing is disabled (error message). In other posts, I read a little about the CORS stuff, but we are using 10.2 Server and the most up to date browsers (tried all 3). So I thought that would not be an issue. We have also disabled the option to "only allow SSL connections" in our AGOLO organization settings but that made no difference.
FYI, I add the service using https://<xxxxx>/securearcgis/rest/services/