tsnet: add new example serving the Tailscale web client

Updates tailscale/corp#13775

Co-authored-by: Sonia Appasamy <sonia@tailscale.com>
Signed-off-by: Will Norris <will@tailscale.com>
Signed-off-by: Sonia Appasamy <sonia@tailscale.com>

tsnet/example/web-client/web-client.go

@@ -0,0 +1,44 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// The web-client command demonstrates serving the Tailscale web client over tsnet.
+package main
+
+import (
+	"flag"
+	"log"
+	"net/http"
+
+	"tailscale.com/client/web"
+	"tailscale.com/tsnet"
+)
+
+var (
+	devMode = flag.Bool("dev", false, "run web client in dev mode")
+)
+
+func main() {
+	flag.Parse()
+
+	s := new(tsnet.Server)
+	defer s.Close()
+
+	ln, err := s.Listen("tcp", ":80")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer ln.Close()
+
+	lc, err := s.LocalClient()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Serve the Tailscale web client.
+	ws := web.NewServer(*devMode, lc)
+	if err := http.Serve(ln, ws); err != nil {
+		if err != http.ErrServerClosed {
+			log.Fatal(err)
+		}
+	}
+}