Change Authorization Scheme on runtime in Oracle APEX

First, make select list item P4_AUTHORIZTION_SCHEMA

that will contain all Authorization available for your APP

use this code as a source

select a.d, a.r from ( select APEX_200200.wwv_flow_lang.system_message('MUST_NOT_BE_PUBLIC_USER') d,'MUST_NOT_BE_PUBLIC_USER' r, 1 from dual union all select APEX_200200.wwv_flow_escape.html(substr(name,1,50)),to_char(id), 1 from APEX_200200.wwv_flow_security_schemes where flow_id = :APP_ID union all

select '{'||APEX_200200.wwv_flow_lang.system_message('NOT_W_ARGUMENT',APEX_200200.wwv_flow_escape.html(substr(name,1,50)))||'}' d, '!'||to_char(id) r, 2 from APEX_200200.wwv_flow_security_schemes where flow_id = :APP_ID order by 3,1) a

and make a process to update the Application's Authorization

UPDATE APEX_200200.wwv_flows SET SECURITY_SCHEME =:P4_AUTHORIZTION_SCHEMA where ID = :APP_ID;