Welcome to the community, @fogel!
Unfortunately I don’t have a good solution for you right now. We are working on this as part of the Streamlit for Teams 1.0k offering which is in limited beta right now and will be rolling out in early 2020.
If you don’t need true authentication, you could just set up a passphrase using st.text_input and only show the app if the answer matches the passphrase you set. It’s not ideal, but if you are just trying to gate access that would work. A related feature request we’re tracking will also enable password text_inputs 640.
Thank you for using Streamlit and we apologize for the delay. We’ve been a bit overwhelmed with the amount of questions coming in since launch.