Using set role inside a function question

Hi All,
I have a function pass in a user login id (p_runas_id) and the it will insert a row into a table after that set role to that pass in id. This function complied fine but getting ERROR: role "p_runas_id" does not exist CONTEXT: SQL statement "SET ROLE p_runas_id" when execute. Any suggestion?

Thank you very much,
Garry

CREATE OR REPLACE FUNCTION set_netid_context(p_runas_id varchar(30))
RETURNS void
AS $$
Declare
v_dm_name varchar(30);
v_runid varchar(30);
v_ora_id numeric;

BEGIN
INSERT INTO obiee_context_audit(context_date, ora_sid, db_user, runas_id)
VALUES (now(), pg_backend_pid(), SESSION_USER, p_runas_id);
SET ROLE p_runas_id;
END; $$
LANGUAGE plpgsql;