The Using a Workflow to control edit of issue fields describes a partial workaround for Field Level Security (JRA-1330).

With the recent decision to not implement JRA-1330, there is a link to the workaround page at the top of the issue.

The documentation in the workaround is correct, but very terse and somewhat hard to understand. It needs improving - extra context, more detail on the steps. All the usual good technical writing things.

Chris Mountford did a support talk on this recently. He would be a good SME, as would I.