How can I make sure a procedure can only be called from an "after logon on database" trigger?

Oracle Enterprise 19c

I have an "after logon on database" trigger (aka LOGON_TRIGGER), that I want to use to call a procedure (aka, SET_FGAC_FOR_USER), to set database session variables to be used by RLS security, but I don't want the SET_FGAC_FOR_USER procedure to be called outside the logon trigger.

I tried to mark SET_FGAC_FOR_USER as ACCESSIBLE BY LOGON_TRIGGER, but it appears it's not possible to have a procedure whitelisted to a logon trigger. I read something about "Since database logon triggers execute at the session level, they cannot directly control access to specific procedures or functions", but I didn't actually find anything in the documentation.