syncthing: Restrict administration to users in group syncthing

- Add syncthing group
- Add validation in syncthing-plinth configuration

* Tested on UI

Signed-off-by: Aakanksha Saini <aakanksa@thoughtworks.com>
Reviewed-by: Sunil Mohan Adapa <sunil@medhas.org>

data/etc/apache2/conf-available/syncthing-plinth.conf

@@ -18,4 +18,7 @@
 <Location /syncthing/>
     Include includes/freedombox-single-sign-on.conf
     ProxyPass http://localhost:8384/
+    <IfModule mod_auth_pubtkt.c>
+        TKTAuthToken "admin" "syncthing"
+    </IfModule>
 </Location>

plinth/modules/syncthing/__init__.py

@@ -27,6 +27,7 @@ from plinth import cfg
 from plinth import frontpage
 from plinth import service as service_module
 from plinth.menu import main_menu
+from plinth.modules.users import register_group
 from plinth.utils import format_lazy
 from .manifest import clients
 
@@ -61,6 +62,8 @@ description = [
 
 clients = clients
 
+group = ('syncthing', _('Administer Syncthing application'))
+
 service = None
 
 
@@ -69,6 +72,7 @@ def init():
     menu = main_menu.get('apps')
     menu.add_urlname(name, 'glyphicon-refresh',
                      'syncthing:index', short_description)
+    register_group(group)
 
     global service
     setup_helper = globals()['setup_helper']