Instructions provided describe the steps to make Oracle external authentication connections (OSA for Oracle) using a Net Service Name. See Knowledge Base article 42269 for more information.
1. Download the (32-bit) Oracle Instant Client from the ESRI Customer Care Portal, and unzip it to a location on the local ArcGIS Desktop machine. Change the name of the folder if desired.
2. Add the Oracle Instant Client path to the beginning of the existing PATH (operating system) Environment Variable.
3. Create a file called 'TNSNAMES.ORA' inside the Oracle Instant Client directory, and add an entry in the file specifying a desired Net Service Name, the Host machine name (with the local domain), and the Service Name.
(ADDRESS = (PROTOCOL = TCP)(HOST = ORASRVR.<yourDOMAINNAME>)(PORT = 1521))
(SERVER = DEDICATED)
(SERVICE_NAME = ORCL)
4. Create a file called 'SQLNET.ORA' inside the Oracle Instant Client directory and add this entry to the file:
SQLNET.AUTHENTICATION_SERVICES = (NTS)
Setting SQLNET.AUTHENTICATION_SERVICES = (NONE) does not suffice.
5. Create an Environment Variable on the Windows operating system called 'TNS_ADMIN' that references the location of the Oracle Instant Client directory.
6. Launch ArcCatalog and make a connection using the Net Service Name and selecting the Operating System Authentication option from the drop-down (the username and password is grayed out).