RFC 2817: "Upgrading to TLS Within HTTP/1.1", explains how to use the Upgrade mechanism in HTTP/1.1 to initiate Transport Layer Security (TLS) over an existing TCP connection.
RFC 2817 – Upgrading to TLS Within HTTP/1.1 erläutert die Benutzung des Upgrade-Mechanismus in HTTP/1.1, um Transport Layer Security (TLS) über eine bestehende TCP-Verbindung zu initialisieren.