Get the main domain of streamlit app on iframe

I have a streamlit application running on an EC2, with Nginx configured so that the application can only be accessed via an iframe from a specific main domain (the streamlit app domain is not accessible if you place the domain directly in the browser), and it is running via a session of tmux attach -t StreamSession

Can I capture the main domain the iframe is on? The idea is, based on the main domain collected, the application content will be dynamic