Creating a Playlist for an Apple Music User - react-native

Question

I've created an app in React Native which allows a user to search for songs, which uses the Apple Music API. So far, so good.
For the next step. What I want to do is use the songs the user has searched for, and let them save them as a playlist in their Apple Music account (assuming they are a subscriber, etc.).
However, there seems to be a lack of documentation and examples on how to do this (at least compared to Spotify - I'm recreating a Spotify App I made in the past).
I'll need to get authorisation from the user, and then use this endpoint: https://developer.apple.com/documentation/applemusicapi/create_a_new_library_playlist, but I can't find out how exactly to do this. Other parts of the API documentation seem to simply state "With proper authorization from the user, you can also create or modify playlists and apply ratings to the user's content." but never actually explain or link to how to get this authorization.
Can anyone point me in the right direction? And let me know if what I'm trying to do is actually possible with Apple Music - it seems like it is, but the way I'm going around in circles, I'm not so sure anymore. Thank you

Answer 1

I don't know if this will help or not (I'm an iOS dev, not a React dev), but here's the call to save a playlist to a user's Music library, in Swift. Maybe it'll help point you in the right direction(?)
If you'd rather not have Swift code polluting your thread, let me know and I'll remove it.
import StoreKit
// ...
// request user token
if let devToken = UserDefaults.standard.string(forKey: "devToken") {
SKCloudServiceController().requestUserToken(forDeveloperToken: devToken, completionHandler: { userToken, _ in
guard let _ = userToken else { return }
self.addPlaylist()
})
}
// add playlist
func addPlaylist() {
MPMediaLibrary.default().addItem(withProductID: "pl.u-065LACYzL34", completionHandler: { _, error in
guard error == nil else {
print("add playlist sad")
return
}
// success
})
}

Answer 2

I've been looking at trying to do this for a while now.
MusicKit JS works in the browser, but since there is no browser in iOS, that's a no-go: there is no Window.musicKit.getInstance(). And I've yet to find any other way to authorize MusicKit, using JavaScript, except for MusicKit JS.
You can access the Apple music Catalog via the API with only a developer token. You can even access (read only) a user's playlist, if it's public and you know the global id, but that's not what we're after here. We want access to a user's Library so that we can do stuff (except delete, because you can't delete stuff through the Apple Music API).
To authorize access to a user's Library in iOS, you need to use StoreKit, per this, and in order to do that with React Native, you need to use Native Modules per this.
The problem about that second bit, is that I got no idea how to do this. I've read a few things, but I'm not connecting the dot's yet.
If you (or anyone) has figured this out, dropping a note with a how-to here would be awesome. If I do figure it out, I'll come back here and post.
Update: I found this article, which comes close to explaining it really well.
The issues I'm having here are that in the Add a React Native iOS Project section, there's an unfinished sentence ("Here we create..."), and I can't seem to find React.xcodeproj when I run through the steps the author has provided.

Answer 3

Additional remarks: you can run Javascript on a Page in Shortcuts but only when you run shortcuts from sharesheet from Safari.
Also, contrary to what you may seen in many tutorials keep in mind that for POST requests a header Music-User-Token has a value without word "Bearer". In GET request using "Bearer" word will also work. I've built webpage to get music-user-token to clipboard and save it to use it in Shortcuts.