TUN-1976: Pass tunnel hostname through header

h2mux/muxreader.go

@@ -11,6 +11,10 @@ import (
 	"golang.org/x/net/http2"
 )
 
+const (
+	CloudflaredProxyTunnelHostnameHeader = "cf-cloudflared-proxy-tunnel-hostname"
+)
+
 type MuxReader struct {
 	// f is used to read HTTP2 frames.
 	f *http2.Framer
@@ -235,6 +239,8 @@ func (r *MuxReader) receiveHeaderData(frame *http2.MetaHeadersFrame) error {
 			if r.dictionaries.write != nil {
 				continue
 			}
+		case CloudflaredProxyTunnelHostnameHeader:
+			stream.tunnelHostname = TunnelHostname(header.Value)
 		}
 		headers = append(headers, Header{Name: header.Name, Value: header.Value})
 	}