CREATE OR REPLACE CONTEXT "Ctx" USING Set_Ctx;

CREATE OR REPLACE PROCEDURE Set_Ctx( cName IN VARCHAR2, cValue IN VARCHAR2 ) AS
BEGIN
  dbms_session.set_context( '"Ctx"', cName, cValue );
END;
/
BEGIN
  Set_Ctx( 'f2_value', 'ABC' );
END;
/
SELECT sys_context( '"Ctx"', 'f2_value' ) FROM dual;

Connected to Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 
Connected as u99

SQL> CREATE OR REPLACE CONTEXT "Ctx" USING Set_Ctx;

Context created

SQL> CREATE OR REPLACE PROCEDURE Set_Ctx( cName IN VARCHAR2, cValue IN VARCHAR2 ) AS
  2  BEGIN
  3    dbms_session.set_context( 'Ctx', cName, cValue );
  4  END;
  5  /

Procedure created

SQL> BEGIN
  2    Set_Ctx( 'f2_value', 'ABC' );
  3  END;
  4  /

BEGIN
  Set_Ctx( 'f2_value', 'ABC' );
END;

ORA-01031: привилегий недостаточно
ORA-06512: на  "SYS.DBMS_SESSION", line 130
ORA-06512: на  "U99.SET_CTX", line 3
ORA-06512: на  line 2

SQL> SELECT namespace FROM dba_context WHERE "SCHEMA" = USER AND "PACKAGE" = 'SET_CTX';

NAMESPACE
---------------------------------
Ctx

SQL> SELECT sys_context( '"Ctx"', 'f2_value' ), sys_context( 'Ctx', 'f2_value' ) FROM dual;

SYS_CONTEXT('"CTX"','F2_VALUE'                   SYS_CONTEXT('CTX','F2_VALUE')
------------------------------------------------ -------------------------------------------------

SQL>