$ luarocks install mjolnir.lb.spotify
local spotify = require "mjolnir.lb.spotify"
After requiring, usage is super simple. Bind a few Spotify actions to some hotkeys. For me, my keyboard has pause, play, and next commands, so displaying the current song is the main thing I need. To accomplish that, it's just a matter of something like this:
hotkey.bind(mash, 'space', spotify.displayCurrentTrack)
Full documentation should be included in Dash's "Mjolnir" docset.