Help with column-level RLS

Question

So I've started trying column-level RLS. But I don't know how to write the Function. Can somebody help?
I want users in the same office and dept to see full details about the employees in their office, but masked fname, lname, salary of employees in other offices and depts.
-- Table:
'emp' contains columns: fname, lname, address, city, office, dept, position, salary
'user' contains columns: username, office, dept
-- Policy:
BEGIN
DBMS_RLS.ADD_POLICY(object_schema=>'appschema',
object_name=>'emp',
policy_name=>'emp_privacy_policy',
function_schema=>'appschema',
policy_function=>'emp_privacy',
sec_relevant_cols=>'lname, fname, salary',
sec_relevant_cols_opt=>dbms_rls.ALL_ROWS);
END;
-- Function:
CREATE OR REPLACE FUNCTION emp_privacy (username IN VARCHAR2, office IN VARCHAR2, dept IN VARCHAR2)
RETURN VARCHAR2 AS
con VARCHAR2 (200);
BEGIN
con := 'dept = (select dept from USER where username = nvl(v(''APP_USER''),USER) AND office = (select office from USER where username = nvl(v(''APP_USER''),USER)';
RETURN (con);
END emp_privacy;

Answer 1

Look at the demos in Morgan's Library under DBMS_FGAC at www.psoug.org.
Then just follow the examples to build your own.