ipn: add auth key

Signed-off-by: David Crawshaw <crawshaw@tailscale.com>

ipn/backend.go

@@ -90,7 +90,10 @@ type Options struct {
 	//  - StateKey!="" && Prefs!=nil: like the previous case, but do
 	//    an initial overwrite of backend state with Prefs.
 	StateKey StateKey
-	Prefs    *Prefs
+	// AuthKey is an optional node auth key used to authorize a
+	// new node key without user interaction.
+	AuthKey string
+	Prefs   *Prefs
 	// LegacyConfigPath optionally specifies the old-style relaynode
 	// relay.conf location. If both LegacyConfigPath and StateKey are
 	// specified and the requested state doesn't exist in the backend

ipn/local.go

@@ -220,6 +220,7 @@ func (b *LocalBackend) Start(opts Options) error {
 		Logf:            logger.WithPrefix(b.logf, "control: "),
 		Persist:         *persist,
 		ServerURL:       b.serverURL,
+		AuthKey:         opts.AuthKey,
 		Hostinfo:        hi,
 		KeepAlive:       true,
 		NewDecompressor: b.newDecompressor,