Reimplement clientId and clientSecret auth mechanism as fallback option

[binaryben]

Had a thought after reading this comment in #2494. Could it be worth putting the old auth mechanism back in and leaving it in as a reliable fallback option?

It's likely to always be a game of cat and mouse now to keep an auth flow with a nice UX up and running. It's not going to be sustainable to have a flood of issues and one dev working until 2am each time there is an upstream change in this domain.

If there is a known working fallback option that is documented (can even be displayed automatically if issues are detected), the dev can sleep. More importantly, solutions (hacks) to upstream changes are not immediately found.

Then we (users and contributors) wait an agile cycle or two so that Spotify moves on and has time to assume it's working before circumventing. Otherwise, they will just address the bypass right away (as we may be seeing them working on now)