I have a reverse proxy server setup at my.mydomain.com which accepts traffic on port 80 and passes it to myInternalServer:internalPort (let's call it port 4545).
Everything works fine as far as accessing unsecured services go. When trying to log into to the REST login page by going to my.mydomain.com/arcgis/rest/login (by clicking the login link on the upper right)
I get the login page, when look at the page source, I notice that the redirect for the button is my.mydomain.com:4545/arcgis/rest/services which is wrong. When I my server using the internal address myInternalServer:4545/arcgis/rest/login all is well and I can log in.