Community Cloud authentication: is X-Streamlit-User a supported fallback?

Welcome to the community and thanks for your thoughtful question! You’re absolutely right: as of Streamlit 1.42.0, st.user no longer exposes the Community Cloud account email, and this is now the documented and intended behavior. The rationale for this change was primarily privacy and security—ensuring that user identity information is only available when an explicit authentication flow (via OIDC and st.login ) is configured by the app developer, rather than being implicitly exposed by the platform.