Can I use a port-redirect in Apache as a security layer?
The apache proxy seems a viable solution (if that meets your needs for login security). You could probably use iptables to do a port forward from that server port (using localhost probably?) to port 80 on apache. This way nobody will be able to access it directly.
I'm not an expert web app developer. I have an IPython Notebook server running on some port. The in-built security is not great -- one global password can be set, no support for multiple users or for integrating with (e.g.) active directory or OpenID.
I believe I can use an Apache port redirect to control access. e.g. put a firewall up over the port so external users can't go straight to the notebook, but rather they have to go via port 80 as served by Apache. 
Is there some way to write a login page which provides multi-user authentication, then only pass authorised users through to the notebook server?
I apologise in advance if I have used the wrong terminology or glossed over important details.