I actually thought they supported it officially. Seems like it's made by their engineers in their spare time though:
"Spotify for Linux is a labor of love from our engineers that wanted to listen to Spotify on their Linux development machines. They work on it in their spare time and it is currently not a platform that we actively support." [1]
"Spotify for Linux is a labor of love from our engineers that wanted to listen to Spotify on their Linux development machines. They work on it in their spare time and it is currently not a platform that we actively support." [1]
[1] https://www.spotify.com/us/download/linux/