Setting permission based on column

Since there's no possibility to grant/revoke permission on column basis, I'm thinking about trigger that could help in setting some kind of security checking if user is allowed to insert value in column of table. I.e. I have table with columns A,B,C and want only user with role "ABC_ROLE" to have the ability (from Oracle Forms app) to insert/update value in column B. This trigger should be raised before real inserting new row but don't know how to check if user has ABC_ROLE? Finally, need yours ideas, how should this trigger look like?

--

Stjepan Brbot <Stjepan.Brbot_at_ZG.HiNet.HR>