[Zope3-dev] Mini-proposal: new principal interface in zope.security for full closure of group membership

[Gary Poster]

Primary problem:
We frequently want to know the full closure of group membership.  The  
groups attribute of zope.security.interfaces.IGroupAwarePrincipal is  
a list of groups to which the principal directly belongs.  The full  
closure--including the groups to which the principal's groups belong,  
for instance--must be calculated by any piece of code that needs it.

Secondary problem:
The description of  
zope.security.interfaces.IGroupAwarePrincipal.groups does not  
sufficiently clarify that it is *not* a full closure.

Consideration:
zope.security.interfaces.IGroupAwarePrincipal has been around for  
awhile, and probably should not be materially changed (i.e., to  
redefine or add an attribute).

Solution:

1) Clarify the zope.security.interfaces.IGroupAwarePrincipal.groups  
description: change from
"List of ids of groups the principal belongs to"
to
"List of ids of groups to which the principal directly belongs"

2) Add an additional interface to zope.security.interfaces interface.

class IGroupClosureAwarePrincipal(IGroupAwarePrincipal):
     allGroups = interface.Attribute(
         'a readonly iterable of the full closure of the principal's  
groups.')

3) Make the principals in zope.app.authentication implement  
IGroupClosureAwarePrincipal.  First cut of 'allGroups' would probably  
be to make it be a lazy property, returning a tuple of the full closure.

Risks:
Some might be unhappy that allGroups is not a hook point, but a  
convenience: that is, it will be a full closure, not an opportunity  
to be clever to redefine how group membership is calculated.

Thoughts?

Gary