Allow Target Service for specific proxy users/groups only in UTM 9.3

So I need to allow a target service for specific proxy users / groups in UTM 9.3. 

I found how to globally allow a target service here 'Target Service Not Allowed' error in Astaro Security Gateway or here https://community.sophos.com/products/unified-threat-management/astaroorg/f/55/t/46265

Thing is, I don't want to allow that target service for every user but a specific subset of users. How would I do that?

Thanks
Tom

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