Support feature request for device authorization grant flow

[hansmbakker]

Spotify already has a Device Authorization Grant flow that it uses for its TV applications.
This flow is less cumbersome than the redirect url-based flows that it offers for custom applications, and it is meant for headless devices or devices that have a limited support for user input.
Also, it is simpler than the zeroconf-based login flow.

Unfortunately Spotify seems to work with an allowlist for client_id's that can use this flow.

I described how the flow works and requested that Spotify allows all custom applications to use this flow in https://community.spotify.com/t5/Spotify-for-Developers/Device-Authorization-Grant-authentication-flow-for-custom/m-p/5485468 - maybe people from here are interested in the same :)