Share songs as ringtone like garageband

Lastly I've seen a way that we can easily assign musics and songs as ringtone in iPhone directly with Garageband app. With this app you can make m4r files and share it with iOS like below image.

For further reading you can go to this link.

Is it possible with documented APIs?
Does it need any permission or entitlement from Apple?

I'd like to ask any help that can lead me to share sheet like above.

Solution

I contacted Apple about this and they confirmed that it is not possible.

Our engineers have reviewed your request and have concluded that there is no supported way to achieve the desired functionality given the currently shipping system configurations.

So, to answer your question:

No, it is not currently possible to do with documented APIs (as of iOS 11, May 2018).
There isn't a public entitlement or permission that you can request from Apple to use this private API.