Splash page when users access Power BI Report Server web interface?

I want to add a basic "proprietary content" splash page that people have to click "ok" on before accessing reports. I have not been able to find anything online that describes how to create this splash page and how to make it open when people go to the web interface URL. Any help would be greatly appreciated! (I am using a standalone server with no internet access and users also do not have internet access, so it all has to happen on the internal network)