I have a working Sophos UTM9 proxy. THe clients get the proxy configuration via gpo and authenticate against the proxy with SSO. That's work fine. Except spotify dekstop app. It cannot connect using Auto detect settings (which means use the system wide settings, the same you can see under IE proxy settings). If I change it to no proxy/ http proxy/socks4 or socks5 the result is the same. App cannot connect.
Is there any specified port / url spotify use to connect? I monitored the communication on the proxy level but there was no denied request.
The solution regarding touching the proxy is not working (i deployed the proxy corporate wide by reason, so turning it of is not an option). I can create exceptions on the proxy level if there is a list of required hosts and/or ports, but found no documents about it.
Or change to google play instead of spotify