SSRS in Reporting (End-user can design report) and several Problems?

Multi tool use
SSRS in Reporting (End-user can design report) and several Problems?
For example: End-user(customer) can create new report or add/remove columns. I know that SSRS(SQL Server Reporting Service) can do this with "Report-Builder".
The problem is Report-Builder need "ConnectionString" to operate. (I really don't want to share it for end-user).
the second problem is End-user A can override any reports of End-user B with out permission.
In my case, I have a Web app (MVC ASP.Net) and I want to give my customer can design their own reports by simple Interface.
So, How do i do that ? if you suggest any solution, I'm kindly welcome and many thanks.
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