Some limitations but it works (here's how): – Alarm Clock for Spotify Review

The app works but has specific requirements: Spotify premium account connected, notifications enabled, do not disturb off, AND the app must be running WITH THE CLOCK DISPLAYING (that is, not on the settings or alarm set-up screen). I had to do a lot of troubleshooting to figure that out...but it works. Be aware of what's required before you download or give up. Apple Music was buggy and inconsistent in my experience, but when I switched to Spotify, I missed being able to easily play choice music without purchasing individual tracks or albums. This is a decent work-around.
Review by Audible Silence on Alarm Clock for Spotify.