If the user does not type a logon name, then OS authentication is triggered, unless OS authentication is explicitly turned off in the NQSConfig.INI file. For more information, refer to Oracle Business Intelligence Enterprise Edition Deployment Guide. Additionally, OS authentication is not used for Oracle BI Presentation Services users.
The Oracle BI Server populates session variables using the initialization blocks in the desired order that are specified by the dependency rules defined in the initialization blocks. If the server finds the session variable USER, it performs authentication against an LDAP server or an external database table, depending on the configuration of the initialization block with which the USER variable is associated.