connect to the same database with 2 different users

This is a real issue and I treat it as a bug. 
If I have different reports with own datasets in different workspaces why the connection to the same database is always goes using one of the connection string?  
Why do you have a different dataset at all in such case? Just allow only one. I suspect your internal optimization to reduce the number of connections caused this issue, but it should check additionally authorization parameters, not only database name and server.

I want to restrict access to the sensitive data in multitenant SaaS application which uses the same database shared schema and I have no choice. And please don't offer me Row-Level Security, because report designer in such case have access to the data which he shouldn't.
This is really weird when cloud multitenant SaaS application designed in a way to the on-premise app. This is not "cloud-first" approach.