You haven't narrowed down the problem to the point where you should be worrying about how to express what you need with BackgroundTransfer APIs yet - you need to figure out what you need to express, first.
If you have access to good documentation or a knowledgeable owner of this internal service you're connecting to, your first step should be consulting that to figure out what exactly the HTTP request (and the associated credential headers) should look like.
If you don't have access to that, the second best starting point is to take an existing, working client of this service you're uploading to and use a networking capture software (Fiddler, for example) to take a look at what the request it's sending looks like.
Once you've figured out the specific HTTP method and server credentials you need to use, you can tell BackgroundTransfer to use them by setting the method
and serverCredential
properties of your uploader
object before creating your uploads.