custom AccessManager: overwrite isGranted() or checkPermissions()

[stephan lohwasser]

hi,
i am currently working on an own AccessManager-implementaion based on 
acls. (first of all: is there any prior art, or are examples availible?)
to to this i wrote my own access manager which subclasses the simple 
access manager.
the question is: shall i overwrite isGranted() or checkPermissions()? 
which of the methods is called when accessing the repository? or doesn't 
it matter at all? or do i have to overwrite both? or is this the 
completely wrong way?

thanks a lot
stephan