mTLS not working on R2-backed site

I’ve enabled mTLS for a website. If I specify a host that is a regular proxied A or CNAME record, it works fine. However, if I specify an R2-backed host, it doesn’t prompt for the client certificate in the TLS handshake.

I could find this documented as a limitation anywhere. Anyone have any insights?

Correction: “I could NOT find this documented…”