Copied from legacy servers, with some minor futzing to retrieve assets
from wwtassets.org. I needed to configure nginx to return the right
content-type for this ASPX file -- there's a slim chance that maybe
we'll need to become cleverer if we ever get a different ASPX file that
wants to return a different content-type.
As documented in the README, it turns out that the App Service / App Gateway
setup create issues for the domain names in our redirects. Issuing redirects
is an important part of why we have this nginx server anyway, so I've set
something up that tries to Do The Right Thing. It's annoyingly complicated but
I can't devise anything cleaner.