Comment 4 for bug 741186

There aren't many actions in that file. You can just change "no" and "allow_admin_keep" for the org.freedesktop.systemtoolsbackends.set action to "yes", and manual authentication won't be required. The lines to edit are:
  <action id="org.freedesktop.systemtoolsbackends.set">
    <description gettext-domain="system-tools-backends">Manage system configuration</description>
    <message gettext-domain="system-tools-backends">You need to authenticate to modify the system configuration</message>
    <defaults>
      <allow_inactive>no</allow_inactive>
      <allow_active>auth_admin_keep</allow_active>
    </defaults>
  </action>

But this is assuming you can do that change only on trusted test machines or in virtual hosts, because it means any user will be able to run those actions, including changing the root password and things like that... :-(