I has the same as original problem after latest update to 10.10.3
killing the authd as this:
sudo pkill -HUP authd
and checking with the terminal and 'ps -ef | egrep "authd|securityd" showed that is was restarted immediately. But this did not change the behavior.
Then I tried the same with the target of securityd,
sudo pkill -HUP securityd
afterwards, it is still not running, but then I did not check before hand and so I don't know whether it WAS running previously. But there is a new behaviour>
When I click the lock icon to unlock access to change the Sys Preferences, it does NOT respond at all - no brief message about authenticating.
That what I get for poking around in the dark :-)
A system reboot will be happening as soon as convenient (reach a good stopping point).