Where to find "loginReference"?

I asked a similar question some time ago for basic understanding and didn't get too far. However I did find this article by Jason Rahm indicating to use the login provider 'tmos', which instructs the API to use the provider(s?) configured in TMOS. That got me running with token auth, which was required since we used an external authentication provider. Since then I've kinda pushed the "I believe" button and driven on.

If I have time tomorrow I'll look at the SDK code to see what it is doing.