cmd/tailscale: add the renew command

cmd/tailscale/cli/cli.go

@@ -199,6 +199,7 @@ change in the future.
 			debugCmd,
 			driveCmd,
 			idTokenCmd,
+			renewCmd,
 		},
 		FlagSet: rootfs,
 		Exec: func(ctx context.Context, args []string) error {

cmd/tailscale/cli/renew.go

@@ -0,0 +1,78 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package cli
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"os/signal"
+	"strings"
+	"syscall"
+
+	"github.com/peterbourgon/ff/v3/ffcli"
+)
+
+var renewCmd = &ffcli.Command{
+	Name:       "renew",
+	ShortUsage: "tailscale renew",
+	ShortHelp:  "Reauthenticate and renew the device key",
+
+	LongHelp: strings.TrimSpace(`
+HIDDEN: "tailscale renew" triggers reauthentication and renewal of the
+device key.)
+`),
+	FlagSet: upFlagSet,
+	Exec: func(ctx context.Context, args []string) error {
+		return runRenew(ctx)
+	},
+}
+
+func runRenew(ctx context.Context) (retErr error) {
+	st, err := localClient.Status(ctx)
+	if err != nil {
+		return fixTailscaledConnectError(err)
+	}
+	origAuthURL := st.AuthURL
+
+	watchCtx, cancelWatch := context.WithCancel(ctx)
+	defer cancelWatch()
+	watcher, err := localClient.WatchIPNBus(watchCtx, 0)
+	if err != nil {
+		return err
+	}
+	defer watcher.Close()
+
+	go func() {
+		interrupt := make(chan os.Signal, 1)
+		signal.Notify(interrupt, syscall.SIGINT, syscall.SIGTERM)
+		select {
+		case <-interrupt:
+			cancelWatch()
+		case <-watchCtx.Done():
+		}
+	}()
+
+	if err := localClient.StartLoginInteractive(ctx); err != nil {
+		return fmt.Errorf("could not call localapi: %w", err)
+	}
+
+	for {
+		n, err := watcher.Next()
+		if err != nil {
+			return err
+		}
+		if n.ErrMessage != nil {
+			msg := *n.ErrMessage
+			fatalf("backend error: %v\n", msg)
+		}
+		if url := n.BrowseToURL; url != nil && *url != origAuthURL {
+			fmt.Fprintf(Stderr, "\nTo authenticate, visit:\n\n\t%s\n\n", *url)
+		}
+		if n.LoginFinished != nil {
+			fmt.Fprintf(Stderr, "Success.\n")
+			return nil
+		}
+	}
+}