I'm trying to understand the information at https://developer.sonos.com/build/content-service-add-features/add-authentication/use-authentication-tokens/
There's an "auth token" and there's a "private key" (from getDeviceAuthTokenResponse) which seems to be variously termed "key" and also "refresh token".
I think I understand the purpose for refresh tokens in general (i.e. something that lives forever, but isn't passed around often and isn't passed around to just everyone), but the first section in that URL above seems to indicate that the auth token and the key are both passed to just about every request.
Why should tokens be short-lived when the key, which is long-lived, is passed along in parallel, it seems. Why not then just not populate the initial private key and let the auth token live forever?
What am I missing? Are the token and private key (aka refresh token) NOT actually passed together everywhere, or is the operative word that the very original private key only ever passed (which the server can choose to change but seems pointless to include it, in the end)