Some requests fail to include Authorization header

[andrewazores]

See #397 (comment)

Some HTTP requests made by the Api.service.tsx do not include the appropriate Authorization header, and so only work in a basic development testing loop where no auth is enabled. The bug appears to manifest for methods that attempt to set other headers in the request, such as a Content-Type, and this additional header is incorrectly merged with the normally generated login service headers, which include Authorization and X-JMX-Authorization.