I don't believe how insecure this is, I'm actually a student in a uni accommodation and one of my friends have spotify installed on his xbox one and I found out that my account was on his xbox because of spotify connect without asking for username or password
that's just insecure and I'm not going to stay on premium service or even spotify after that
Spotify takes all reports about security very serious. You can login on your Xbox One, with another device that has been logged in with your Spotify account, and by selecting your Xbox in the Devices Overview. It's only possible to login on Xbox One, with a device that already has been logged in or with your username and password. Let me know if you have any other questions.