Purpose of this parameter found in sqlnet.ora file:
Use the parameter SQLNET.AUTHENTICATION_SERVICES to enable one or more authentication services. If authentication has been installed, it is recommended that this parameter be set to either none or to one of the authentication methods.
Authentication Methods Available with Oracle Net Services:
* none for no authentication methods. A valid username and password can be used to access the database.
* all for all authentication methods
* nts for Windows NT native authentication
Authentication Methods Available with Oracle Advanced Security:
* kerberos5 for Kerberos authentication
* cybersafe for Cybersafe authentication
* radius for RADIUS authentication
* dcegssapi for DCE GSSAPI authentication
When it is set to NTS, which should only be set on Windoze, it allows users to be authenticated using Windows NT native security. What this means is that by setting SQLNET.AUTHENTICATION_SERVICES to NTS and a creating a role called ORA_DBA with your user in that group you should be able to log in to oracle without supplying a password. (connect / as sysdba)