You shouldn't need to add any headers. The coreflow doesn't directly interact with the network call that calls your core, that is done by Host Adapter down stream. The Bridge/Host Adapter should take care of that for you. Is there a specific reason you need a header, or are you seeing any failures in your testing that would lead to thinking a header is necessary?
Yes, the issue that I continue to run into is a 500 Internal Server error. I've tried to improve the logging as much as possible, but my team internally said that Q2 has gone through the natting process for our JXchange environment, and I can't find out whether or not I need to send username and password variables via the xml in the request. Currently when I log the request from request = await self.core.build_start_workflow(acctId, custId), it appears to be empty even though I have validated the syntax