If I understand well, then you are looking for a kind of anonymous access to the report, right? Or deal with the authentication on your web application side. You may want to take a look at Power BI Embedded, which was released two weeks ago. In a nutshell it does the same as the regular app, but takes away the user authentication against Power BI web service. It authenticates only the app, and not the user. This way your end user will never face the Azure authentication pages at all.
I hope that helps.