Get POST from iframe (streamlit component)

Hi,
If i render html+js form in iframe - how can I get data from it? F.e.
I use this lib for the questionnaire - Questions — Questions 0.1.0 documentation

I render it using

import streamlit.components.v1 as components
components.html(…)

How can I get data from it? Here is default way with Flask for example (not from iframe)
https://questions.readthedocs.io/en/latest/usage.html#accessing-form-data

Thank you!