Hi Theo,
The proxy makes it so they don’t have to log in, the rules pass that to the web page and “log in” automatically for the user. It’s the only way to keep your map / layers secure, without resorting to buying hundreds of user accounts (and making everyone log in every time, that wouldn’t go over well here). I wouldn’t just publish it to everyone and hope no one outside sees it, that’s kinda risky (our attorneys wouldn’t be happy if I did that). Portal is another solution, then you could keep the data from going outside your firewall, so sharing with everybody shouldn’t be an issue in that scenario.
I am trying to get this proxy set up myself, ESRI support has been helping me since I can’t get it working, but once we get it done, it should be done, and other apps I put together should be able to use it as well. I think I’m in the same boat as you, we are a town with over 800 internal users (different map apps, like fire dept, planning/development, public works, etc.) but all users that would need an account without the proxy solution.
Leaving our old environment and getting into this has definitely proved to be a challenge, for sure, in all aspects, from arcgis online to wab to javascript. I am getting through this piece by piece (somewhat) but the user support is really good. I will also read through the workflow from Robert, to see if that will help me get this proxy up and running.
Best of luck Theo,
Jeff