multi: add disable authenticator option

To make it easier to use aperture in a setup where we only need its
proxy functionality but not its LSAT capabilities, we add the option to
disable the authenticator. This makes it possible to run aperture
without needing to connect it to an lnd node.

aperture.go

@@ -161,15 +161,18 @@ func (a *Aperture) Start(errChan chan error) error {
 			Value: price,
 		}, nil
 	}
-	a.challenger, err = NewLndChallenger(
-		a.cfg.Authenticator, genInvoiceReq, errChan,
-	)
-	if err != nil {
-		return err
-	}
-	err = a.challenger.Start()
-	if err != nil {
-		return err
+
+	if !a.cfg.Authenticator.Disable {
+		a.challenger, err = NewLndChallenger(
+			a.cfg.Authenticator, genInvoiceReq, errChan,
+		)
+		if err != nil {
+			return err
+		}
+		err = a.challenger.Start()
+		if err != nil {
+			return err
+		}
 	}
 
 	// Create the proxy and connect it to lnd.
@@ -267,7 +270,9 @@ func (a *Aperture) UpdateServices(services []*proxy.Service) error {
 func (a *Aperture) Stop() error {
 	var returnErr error
 
-	a.challenger.Stop()
+	if a.challenger != nil {
+		a.challenger.Stop()
+	}
 
 	// Shut down our client and server connections now. This should cause
 	// the first goroutine to quit.

config.go

@@ -31,6 +31,8 @@ type AuthConfig struct {
 	MacDir string `long:"macdir"`
 
 	Network string `long:"network"`
+
+	Disable bool `long:"disable"`
 }
 
 type TorConfig struct {