The idea is that in some cases all of your JMX items might use the same authentication data. In other cases it might use different ones.

It would be nice if when you define a JMX host interface you could supply a master username and password for it which was assigned to all jmx items for that host interface.

Then when defining an item for said interface you could tell it to either have its own username and password or for it to inherit the u/p of the interface.