File uploader on azure webapp - 403 Axios Error

@ snehankekre, may I pull you into this discussion? You left very useful advice here: When to use enableCORS and enableXsrfProtection parameters? - :balloon: Using Streamlit - Streamlit
However, I do not fully understand how to implement your solution. What object does self refer to in your case?
e.g. in your answer you describe self.set_header("Access-Control-Allow-Origin", "*"). I would replace the asterisk by my domain, but where do I find this self.set_header?