I have a Spotify app and want to persist basic settings per user between sessions. I see the User object has a username field, so it would be easy to do this using my own backend. My question is, is this allowed, without requiring the user to log in, agree to some TOS, etc? Every app I see that persists any data requires me to log in with Facebook.
Usernames are typically obfuscated out in the Spotify API, so they're not the best thing to use. However, the anonymous ID for the user is the same for a given user/app ID combo across multiple machines, so you could use that instead. This sort of thing is what we designed the anonymous ID for, so you're good to go on the ToS front.
I can't find anything that restricts you from load/storing data from your own servers and I've seen 'you'd have to use your own server' suggested in a number of questions.
Not sure why other apps would involve FB - probably to get more info from the user or promote their product.
You should use the User's URI instead of their username though. I would expect it be more stable than the username and less likely to be little Bobby Tables.
来源：https://stackoverflow.com/questions/22089376/spotify-app-allowed-to-save-user-settings-by-username