Like authorize.conf contains roles and its capabilities information, is there a .conf file which contains splunk native user information which can be edited to create additional users and map them to specific roles?
Locally defined users are stored in $SPLUNK_HOME/etc/passwd. I'm not sure about the format in terms of which fields map to things like role. Rather than trying to edit the file directly in order to add users, you might be better off using supported means like the Python API. There's good documentation on this approach at http://dev.splunk.com/view/python-sdk/SP-CAAAEJ6