Hey Peter!
Streamlit for Teams will let you restrict access to apps to authorized viewers and deploy your app from a private repo in Github.
We’re working on making “secrets” (the ability to securely pass environment variable to your app) available to our free tier users. This opens the door to a couple options (described below) for accessing secure data behind a company VPC. Note that both of these options require network configuration changes on your end.
One option is to expose an endpoint to access your data from the public internet with secured mutual TLS auth (see this, for example: How to create a dual-authentication HTTPS client in Python without (L)GPL libs? - Stack Overflow 4).
The second option builds on the first. In addition to exposing an endpoint, you can create a firewall rule to only allow inbound Streamlit traffic into your network.
Shoot an email to amanda@streamlit.io if you want to learn more about Streamlit for Teams. We have a beta program currently in progress 
Cheers,
James