The Oauth feature is brought with ORDS.
The documentation is quite clear about implementation
ie: for public Apex instance, in order to access to admin interface, launch:
first change "2777385" to something more appropriate.
RESTful Services can be protected with the OAuth2 protocol to control access to nonpublic data to prevent data snooping.It comes out of the box with ORDS. to enable it
Locate the folder where the Oracle REST Data Services configuration is stored.
Edit the file named defaults.xml.
Add the following setting to the end of this file just before the </properties> tag.
Save the file.
Restart Oracle REST Data Services if it is running.
The REST support in APEX is an optional installation during the APEX install prior to setting up the ORDS listener.
Login SYS as SYSDBA and run the following from your <dbhome>/apex directory