Unable to control Chromecast Volume with Spotify in Background

[rsb39]

Simple request - add functionality to the iOS app enabling Chromecast volume control when Spotify is in background (and from iOS lockscreen).

Chromecast volume control works fine when Spotify is in the foreground, but it is cumbersome to open the Spotify app simply to adjust Chromecast volume. 

The YouTube app allows for Chromecast volume control from lockscreen, home screen, etc. 

Please add this functionality for Spotify's iOS + Chromecast users!