How to change Authentication Schemes on runtime in Oracle APEX

 first make select list item  P2_AUTHENTICATION_ID
that will contain all Authentication available for your APP

use this code as source 

select name as d,

       id   as r

  from APEX_200200.wwv_flow_authentications

 where flow_id           = :APP_ID

   and security_group_id = :WORKSPACE_ID

 order by 1

and make process to update Application Authentication 

UPDATE APEX_200200.wwv_flows 

SET AUTHENTICATION_ID =:P2_AUTHENTICATION_ID

where ID = :APP_ID;

--
thanks