Comment 1 for bug 370311

Unfortunately this is not possible due to several reasons.

1) Reading the API, seems like this is too difficult without a GStreamer plugin.
2) Spotify is invitation-only, so it can't be tested by most people.
3) Spotify's restrictive terms of use regarding API keys [1]: "The Application Key must be embedded in your Application ... in a secure manner not accessible by third parties.". All of Exaile's source code is available for anyone to look at, so it can't fulfill this requirement.
4) libspotify is non-free; Exaile can't use it due to licence incompatibility.

[1] http://developer.spotify.com/en/libspotify/terms-of-use/