rc/rcserver: with --rc-files if auth set, pass on to URL opened

If `--rc-user` or `--rc-pass` is set then the URL that is opened with
`--rc-files` will have the authorization in the URL in the
`http://user:pass@localhost/` style.

docs/content/rc.md

@@ -79,6 +79,10 @@ If this is set then rclone will serve the files in that directory.  It
 will also open the root in the web browser if specified.  This is for
 implementing browser based GUIs for rclone functions.
 
+If `--rc-user` or `--rc-pass` is set then the URL that is opened will
+have the authorization in the URL in the `http://user:pass@localhost/`
+style.
+
 Default Off.
 
 ### --rc-no-auth

fs/rc/rcserver/rcserver.go

@@ -69,7 +69,16 @@ func (s *Server) Serve() error {
 	fs.Logf(nil, "Serving remote control on %s", s.URL())
 	// Open the files in the browser if set
 	if s.files != nil {
-		_ = open.Start(s.URL())
+		openURL, err := url.Parse(s.URL())
+		if err != nil {
+			return errors.Wrap(err, "invalid serving URL")
+		}
+		// Add username, password into the URL if they are set
+		user, pass := s.opt.HTTPOptions.BasicUser, s.opt.HTTPOptions.BasicPass
+		if user != "" || pass != "" {
+			openURL.User = url.UserPassword(user, pass)
+		}
+		_ = open.Start(openURL.String())
 	}
 	return nil
 }