Well, Swagger aside, maybe I'm next in line to struggle with CORS. Here's an example of what is going wrong. I make a connection (the $model request I presume), and then I call the Login endpoint and get a JWT, and then I make the Survey call which passes the preflight but not the actual request?
Here's the Survey preflight
The failed request
And the console.log messages telling me what is wrong without telling me what is wrong 
So what causes a preflight to succeed and not the actual request? Status code: 0? If I turn off authentication (remove the [Authorize] attribute in the endpoint) things work fine.