Posting to Facebook without browser access possible with new Device Authentication model possible?
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I have a question regarding "Device authentication" or more an application in a secured environment:

As a service in one of our applications we would like to implement a feature where in a multi-user environment one user can grant "posting" rights to one ore more users for a Facebook page/account without sharing the credentials.
Example:
E.g. UserA has a Business page and allows UserB (employee) to make postings inside our application to his (company) page. UserB can't directly access FB with those credentials and is sand boxed to just make postings via the UI of our application -> It is not supposed to be a full Facebook experience more a convenience to allow posting without switching the computer, and allowing to share highly limited permissions across individuals without exposing credentials.

The problem is, that because of security requirements no browser is allowed to be used inside our application.
I know there is Authentication for Devices currently in Beta testing, and that would ideally work for us: UserA uses that OAuth flow e.g. every 0-60 days (depending on UserA's preference) to (re)authenticate our application and if he grants permission to UserB inside out application, UserB can make posting on the company site (and nothing else).
Since I don't know when/if that authentication flow is available, are there any other ways to achieve this?

Thanks for your help in advance!