This is a very important prerequisite PR for access control features. Very helpful enhancement. I would suggest moving database.py to a common folder under /registry so that sql-based access control can reuse it. Also, are the interface.py and models.py a common description for all backend registries? If so, shall we move those common definition outside of sql-registry?

I plan to submit another following up PR for re-structuring, don't want to mess up before function stabilization.

plan to submit another following up PR for re-structuring, don't want to mess up before function stabilization.

Agree, I can also help to do this my access control PR.