I am trying to reset everyone's login session to force everyone to relogin. Is it possible to do this?
Yeah, just alter the cookie salt in the config. Just pick 1 letter and change it (to any other letter) is the easiest way. As soon as you save it, all logins will end.
So with this line in config.php...
$Configuration['Garden']['Cookie']['Salt'] = 'bf9oCwTa3DAb0rBD';
Just change one of those characters in the salt?
Also, the salt is supposed to be secret. If that was your real one, I'd randomly generate an entirely new one now instead of just changing a character. Not quite as bad as posting your database password online, but not good either.