INTEGRATE POWER BI WITH WEB APPLICATION

I have the following requirement:

We have developed a web application on MS dot Net. there are 1000 customers.

Our middle tier authenticates users based on their client organization and role (admin and operator role) and accordingly gives them access to the web site forms. There is a common DB on Azure for the web app with clients data.

We want to provide our clients, access to the data specific to their role and the client for use in Power BI dashboards. We want to make it a true self served platform.

How do we provide access to the clients with only their data and based on their role.

Can Power BI somehow use the web API pertaining to the web app to allow customers to view the data and create dashboards?

It may be useful to mention that in the web app, there is a reports page (that we have custom built) that allows clients to extract their data in Excel based on their selection of columns. We want the same functionality given on the fly to the users using power BI. How do we do that?

Ex: There are 3 tables - customer contact, customer campaign and customer campaign revenue 

The reuqirement is to enable clients to view only their data, if client is operator he shouldbe able to view customer campaign data also and if the client is admin, he should be able to view all there tables data spcific to the cleint.

Alos, can we use the web applicaiton authentication page to do the authentication for power bi as well?

Thank you