NAME¶
Apache2::SiteControl - Perl web site authentication/authorization system
SYNOPSIS¶
See samples/site for complete example. Note, this module is intended for
mod_perl. See Apache2::SiteControl for mod_perl2.
DESCRIPTION¶
Apache2::SiteControl is a set of perl object-oriented classes that implement a
fine-grained security control system for a web-based application. The intent
is to provide a clear, easy-to-integrate system that does not require the
policies to be written into your application components. It attempts to
separate the concerns of how to show and manipulate data from the concerns of
who is allowed to view and manipulate data and why.
For example, say your web application is written in HTML::Mason. Your individual
"screens" are composed of Mason modules, and you would like to keep
those as clean as possible, but decisions have to be made about what to allow
as the component is processed. SiteControl attempts to make that as easy as
possible.
DEVELOPER'S VIEWPOINT - EXAMPLE¶
In this document we use HTML::Mason to create examples of how to use the control
mechanisms, but any mod_perl based system should be supportable.
A good mason component tries to do most of the perl processing in a separate
block, so that simple substitutions can be made in HTML in the rest of the
page. This makes it much easier for web developers and perl developers to
co-exist on a project.
The SiteControl system tries to make it possible to continue to follow this
model. You obtain a user object and permission manager from the SiteControl
system. These are intended to be opaque data types to the page designer, and
are defined elsewhere (see USERS). The actual web page component should carry
these objects around without implementing anything in the way of policy.
For example, your mason component might look like this:
<HTML>
<HEAD> ... </HEAD>
% if($manager->can($currentUser, "edit", $table)) {
<FORM METHOD=POST ACTION="...">
<P><INPUT TYPE=TEXT NAME="x" VALUE="<% $table->{x} %>">
...
</FORM>
% } else {
<P>x is <% $table->{x} %>
% }
<%init>
my $currentUser = Apache2::SiteControl->getCurrentUser($r);
my $manager = Apache2::SiteControl->getPermissionManager($r);
... application specific stuff...
i.e.
my $table = ...
</%init>
Notice that the component does not bother looking at the user object, and there
is no policy code...just a request for permission:
if($manager->can($currentUser, "do something to", $resource))
Of course the developer needs to know
something about the underlying
system. For example, the action string "do something to" is rather
arbitrary. These can be anything, and must be specified as rule actions. It is
recommended that you use some form of Perl constants for these instead of
strings, but that is up to you.
The resource is intended to be less opaque. This is likely the object that the
page developer wants to muck with, and so probably knows the internals of that
object a bit better. This is the crossover point from what SiteControl can
figure out on its own to information you have to supply.
The default behavior is for the manager to deny any request. In order for a
request to be approved, someone has to write a rule that joins together the
user, action, and resource and makes a decision about the permissibility of
the action.
If all you want is login and user tracking (but no permission manager), then it
is safe to ignore the permission manager altogether.
USERS¶
Users and Rules are the central components of the SiteControl system. The user
object must be Apache2::SiteControl::User (or a subclass). See
Apache2::SiteControl::User for a description of what it supports (session
storage, logout, etc.). The glue to SiteControl is the UserFactory, which you
can define or accept the default of Apache2::SiteControl::UserFactory
(recommended).
Whenever a login attempt succeeds, the factory returns an object that represents
a valid, logged-in user. See Apache2::SiteControl::UserFactory for more
information.
PERMISSION MANAGER¶
Each site will have a permission manager. There is usually no need for you to
subclass Apache2::SiteControl::PermissionManager, but you do need to create
one and populate it with your access rules. You do this by creating a factory
class, which looks something like this:
package samples::site::MyPermissionFactory;
use Apache2::SiteControl::PermissionManager;
use Apache2::SiteControl::GrantAllRule;
use samples::site::EditControlRule;
use base qw(Apache2::SiteControl::ManagerFactory);
our $manager;
sub getPermissionManager
{
return $manager if defined($manager);
$manager = new Apache2::SiteControl::PermissionManager;
$manager->addRule(new Apache2::SiteControl::GrantAllRule);
$manager->addRule(new samples::site::EditControlRule);
return $manager;
}
1;
The primary goal of your factory is to produce an instance of a permission
manager that knows the rules for permitting access to your site. This is an
easy process that involves calling the constructor (via new) and then calling
addRule one or more times.
RULES¶
The PermissionManager is the object that the site developers ask about what is
allowed and what is not. As you saw in the previous section, you create a
manager, and add some rules.
Each rule is a custom-written class that implements some aspect of your site's
access logic. Rules can choose to grant or deny a request. The following is a
pretty complex example that demonstrates the features of a rule.
Most rules with either specifically grant permission, or deny it. Most will not
deal with both possibilities. In this example we are assuming that the user is
implemented as an object that has attributes which can be retrieved with a
getAttribute method (of course, you would have to have implemented that as
well). The basic action that this rule handles is called "beat up",
so the site makes calls like:
if($referee->can($userA, "beat up", $userB)) { ... }
In terms of English, we would describe the rule "If A is taller than B,
then we say that A can beat up B. If A is less skilled than B, then we say
that A cannot beat up B". The rule looks like this:
package samples::FightRules;
use strict;
use warnings;
use Carp;
use Apache2::SiteControl::Rule;
use base qw(Apache2::SiteControl::Rule);
sub grants($$$$)
{
my $this = shift;
my $user = shift;
my $action = shift;
my $resource = shift;
if($action eq "beat up" && $resource->isa("Apache2::SiteControl::User")) {
my ($h1, $h2);
$h1 = $user->getAttribute("height");
$h2 = $resource->getAttribute("height");
return 1 if(defined($h1) && defined($h2) && $h1 > $h2);
}
return 0;
}
sub denies($$$$)
{
my $this = shift;
my $user = shift;
my $action = shift;
my $resource = shift;
if($action eq "beat up" && $resource->isa("Apache2::SiteControl::User")) {
my ($s1, $s2);
$s1 = $user->getAttribute("skill");
$s2 = $resource->getAttribute("skill");
return 1 if(defined($s1) && defined($s2) && $s1 < $s2);
}
return 0;
}
1;
The PermissionManager will only give permission if
at least one rule
grants permission,
and no rule denies it.
I think it is clearer to separate rules like the previous one into separate rule
classes altogether. A HeightMakesMightRule and a DefenseSkillRule. Splitting
into two rules makes things clearer, and there is no limit to the number of
rules that the PermissionManager can check.
It is important that your rules never grant or deny a request they do not
understand, so it is a good idea to use type checking to prevent strangeness.
Assertions should not be used if you expect different rules to accept
different resource types or user types, since each rule is used on every
access request.
EXPORT¶
None by default.
SEE ALSO¶
Apache2::SiteControl::UserFactory, Apache::SiteControl::ManagerFactory,
Apache2::SiteControl::PermissionManager, Apache::SiteControl::Rule
AUTHOR¶
This module was written by Tony Kay, <tkay@uoregon.edu>.
COPYRIGHT AND LICENSE¶
This modules is covered by the GNU public license.