In prior Oracle version you used to be able to hack a users password by using the identified by values syntax. This no longer works in 12c, but there is a hack for the hack as blogged by Brian Peasland.
Here is a quick query that will generate the alter user command:
,'alter user '||u.username||' identified by values '''||s.spare4||''';' cmd
from dba_users u
join sys.user$ s
on u.user_id = s.user#
where u.username = upper('&username');