proxy: 'transparent' also sets X-Forwarded-For (closes #924)

caddyhttp/proxy/upstream.go

@@ -289,6 +289,7 @@ func parseBlock(c *caddyfile.Dispenser, u *staticUpstream) error {
 	case "transparent":
 		u.upstreamHeaders.Add("Host", "{host}")
 		u.upstreamHeaders.Add("X-Real-IP", "{remote}")
+		u.upstreamHeaders.Add("X-Forwarded-For", "{remote}")
 		u.upstreamHeaders.Add("X-Forwarded-Proto", "{scheme}")
 	case "websocket":
 		u.upstreamHeaders.Add("Connection", "{>Connection}")