I am working on a hosted CMS, and am thinking about allow site editors to add custom javascript and html (a much requested feature).
I am concerned that this will open up an attack vector - nasty js could make calls to the functions that our hosted CMS exposes (see the Samy worm for an example of what user scripts did to myspace), but I really want to give users control over their site (what's the point of a CMS you can't add your own clever stuff to?)
What is a good approach to fixing this issue? I can think of several which I would like commentary on, but am not going to list them for fear of the 'no list questions mods'!