Hi there,
Thank you for reaching out to us!
We are trying to reply and provide some information to older posts, in case others find it useful as well.
Retrieving an access token without user interaction is possible through the use of the Client Credentials Flow. You can setup a Machine-to-Machine application ( M2M ) that runs in the background, which will authenticate and authorize the application instead of a user. In this case, a Client ID and Client Secret are required.
This was also previously mentioned in the following topic : Can we obtain Access Token for our API without any authentication happening before?
Hope that helped!
Gerald