O/S authenticated local login without password

Create User

CREATE USER "OPS$OPT_DOMAIN\CYBERARKDBA" IDENTIFIED EXTERNALLY AS 'null'    
DEFAULT TABLESPACE "USERS"
TEMPORARY TABLESPACE "TEMP";
GRANT CREATE SESSION TO "OPS$OPT_DOMAIN\CYBERARKDBA";

Now, you can login to oracle without password

sqlplus /

SQL*Plus: Release 12.2.0.1.0 Production on Fri Aug 10 22:55:51 2018

Copyright (c) 1982, 2016, Oracle.  All rights reserved.


Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

SQL> select user from dual;

USER
--------------------------------------------------------------------------------
OPS$OPT_DOMAIN\CYBERARKDBA