As far as I can tell, recent boinc-client versions force you to have a non-empty gui_rpc_auth.cfg.
On dedicated DC computers on which the utility of a GUI RPC password is questionable, one now needs to ensure that all client instances have the same gui_rpc_auth.cfg (e.g. a symlink to /var/lib/boinc-client/gui_rpc_auth.cfg) and that this file is readable by all users who control boinc. This should work for boinccmd and boincmgr.
But as far as I understand, that doesn't work for boinctui and BoincTasks. There you apparently need to enter the password separately in the respective configuration dialogues, or edit the underlying xml config files.
On dedicated DC computers on which the utility of a GUI RPC password is questionable, one now needs to ensure that all client instances have the same gui_rpc_auth.cfg (e.g. a symlink to /var/lib/boinc-client/gui_rpc_auth.cfg) and that this file is readable by all users who control boinc. This should work for boinccmd and boincmgr.
But as far as I understand, that doesn't work for boinctui and BoincTasks. There you apparently need to enter the password separately in the respective configuration dialogues, or edit the underlying xml config files.