Mix of users for service and SQL

What is a one sentence summary of your feature request?

A mix of users for service and SQL is needed.

Please describe your idea in detail. What is your problem, why do you feel this idea is the best solution, etc.

A mix of users for service and SQL is needed.
It is not possible to e.g. use
service: local system + SQL user: AD user
or
service: AD user 1 + SQL user: AD user 2
That should be supported.

How do you currently solve the challenges you have by not having this feature?

choose one working combination