Git and securing a repository

I've been using git for some time and love it.  For open source projects 
there's clearly nothing currently better.

However, I am now using git for proprietary elements, which in the 
future I may need or want to partially restrict access to.  The idea 
being that at my company some (junior) developers should not be given 
access to some elements.  That means either that some full git 
repository should be password protected or even portions of the same 
repository.

Another desirable way to protect elements might be only giving 
clone/pull access to a repository (or portion of it) but not permissions 
to push in changes.

I have not seen or read much about how git deals with accesses and 
permissions.  Can anyone point me to some documentation if some or all 
of this is possible?


-- 
Gonzalo Garramuño
ggarra@advancedsl.com.ar

AMD4400 - ASUS48N-E
GeForce7300GT
Xubuntu Gutsy