RFC 7615 HTTP Authentication-Info and Proxy-Authentication-Info Response Header Fields
Superseded. What governs this material today:
- obsoleted by RFC 9110 — HTTP Semantics
This specification defines the "Authentication-Info" and "Proxy- Authentication-Info" response header fields for use in Hypertext Transfer Protocol (HTTP) authentication schemes that need to return information once the client's authentication credentials have been accepted.
Not ingested in full here — read it on rfc-editor.org.