The spotify service offers several proprietary ways to access their streaming services, those are documented on the spotify page. This page gathers the details of FOSS alternatives.
The mopidy music software (already in Debian) has support for spotify, but it requires:
the mopidy-spotify plugin. However, by default it requires
libspotify - a source available library, which uses an API provided by the Spotify company(which still exists, but is deprecated and also requires applying for an application key). The libspotify library has their API key hard coded in the source. Maybe it would be possible for this to go in contrib/non-free?
There is also mopidy-spotify-tunigo which is a plugin for browsing spotify.
These are available from their apt repository
RFP for despotify - a FOSS client, requires a premium spotify account to work.
RFP for libopenspotify - intended to be a FOSS drop-in replacement for libspotify
RFP for spokify - a KDE client for spotify, needs libspotify or libopenspotify
RFP for playerctl - a command-line controller and library for mpris streaming sources (including spotify