view release on metacpan or  search on metacpan

lib/Abilities.pm  view on Meta::CPAN

=head1 VERSION

version 0.5

=head1 SYNOPSIS

	package User;
	
	use Moose; # or Moo
	with 'Abilities';
	
	# ... define required methods ...
	
	# somewhere else in your code:

	# get a user object that consumed the Abilities role
	my $user = MyApp->get_user('username'); # $user is a User object

	# check if the user is able to do something
	if ($user->can_perform('something')) {
		do_something();
	} else {
		die "Hey you can't do that, you can only do " . join(', ', keys %{$user->abilities});
	}

=head1 DESCRIPTION

Abilities is a simple yet powerful mechanism for authorizing users of web
applications (or any applications) to perform certain actions in the application. This is an
extension of the familiar role-based access control that is common in
various systems and frameworks like L<Catalyst> (See L<Catalyst::Plugin::Authorization::Roles>
for the role-based implementation and L<Catalyst::Plugin::Authorization::Abilities>
for the ability-based implementation that inspired this module).

As opposed to role-based access control - where users are allowed access
to a certain feature (here called 'action') only through their association
to a certain role that is hard-coded into the program - in ability-based
acccess control, a list of actions is assigned to every user, and they are
only allowed to perform these actions. Actions are not assigned by the
developer during development, but rather by the end-user during deployment.
This allows for much more flexibility, and also speeds up development,
as you (the developer) do not need to think about who should be allowed
to perform a certain action, and can easily grant access later-on after
deployment (assuming you're also the end-user).

Abilities to perform certain actions can be given to a user specifically, or
via roles the user can assume (as in role-based access control). For example,
if user 'user01' is a member of role 'admin', and this user wishes to perform
some action, for example 'delete_foo', then they will only be able to do
so if the 'delete_foo' ability was given to either the user itself or the
'admin' role itself. Furthermore, roles can recursively inherit other roles;
for example, the role 'mega_mods' can inherit the roles 'mods' and 'editors'.
Users of the 'mega_mods' role will assume all actions owned by the 'mods'
and 'editors' roles.

A commonly known use-case for this type of access control is message boards,
where the administrator might wish to create roles with certain actions
and associate users with the roles (more commonly called 'user groups');
for example, the admin can create an 'editor' role, giving users of this
role the ability to edit and delete posts, but not any other administrative
action. So in essence, this type of access control relieves the developer
of deciding who gets to do what and passes these decisions to the
end-user, which might actually be necessary in certain situations.

The C<Abilities> module is implemented as a L<Moo role|Moo::Role> (which makes
it compatible with L<Moose> code). In order to be able to use this mechanism,
applications must implement a user management system that will consume this role.
More specifically, a user class and a role class must be implemented, consuming this role. L<Entities> is a reference implementation that can be used by applications, or
just taken as an example of an ability-based authorization system. L<Entities::User>
and L<Entities::Role> are the user and role classes that consume the Abilities
role in the Entities distribution.

=head2 CONSTRAINTS

Generally, an ability is a yes/no option. Either the user can or can't perform
a specific action. At times, this might not be flexible enough, and the user's
ability to perform a certain action should be constrained. For example, a user
might be granted the ability to edit posts in a blog, but this ability should
be constrained to the user's posts only. The user is not to be allowed to edit
posts created by other users. C<Abilities> supports constraints by allowing to
set a name-based constraint when granting a user/role a certain ability. Then,
checking the user's ability to perform an action can include the constraint,
for example:

	if ($post->{user_id} eq $user->id && $user->can_perform('edit_posts', 'only_his')) {
		# allow
	} else {
		# do not allow
	}

Here, the C<Abilities> module allows you to check if the user's ability is constrained,
but the responsibility for making sure the constraint is actually relevant
to the case is left to you. In the above example, it is the application that
checks if the post the user is trying to edit was created by them, not the C<Abilities>
module.

=head2 (PAID) SUBSCRIPTION-BASED WEB SERVICES

Apart from the scenario described above, this module also provides optional
support for subscription-based web services, such as those where customers
subscribe to a certain paid (or free, doesn't matter) plan from a list
of available plans (GitHub is an example of such a service). This functionality
is also implemented as a Moo(se) role, in the L<Abilities::Features> module provided
with this distribution. Read its documentation for detailed information.

=head1 REQUIRED METHODS

Classes that consume this role are required to implement the following
methods:

=head2 roles()

Returns a list of all role names that a user object belongs to, or a role object
inherits from.

Example return structure:

	( 'moderator', 'supporter' )

NOTE: In previous versions, this method was required to return
an array of role objects, not a list of role names. This has been changed
in version 0.3.

=cut

requires 'roles';

=head2 actions()

Returns a list of all action names that a user object has been explicitely granted,
or that a role object has been granted. If a certain action is constrained, then
it should be added to the list as an array reference with two items, the first being
the name of the action, the second being the name of the constraint.

Example return structure:

	( 'create_posts', ['edit_posts', 'only_his'], 'comment_on_posts' )

NOTE: In previous versions, this method was required to return
an array of action objects, not a list of action names. This has been changed
in version 0.3.

=cut

requires 'actions';

=head2 is_super()

This is a boolean attribute that both user and role objects should have.
If a user/role object has a true value for this attribute, then they
will be able to perform any action, even if it wasn't granted to them.

=cut

requires 'is_super';

=head2 get_role( $name )

This is a method that returns the object of the role named C<$name>.

=cut

requires 'get_role';

=head1 PROVIDED METHODS

Classes that consume this role will have the following methods available
to them:

=head2 can_perform( $action, [ $constraint ] )

Receives the name of an action, and possibly a constraint, and returns a true
value if the user/role can perform the provided action.

=cut

sub can_perform {
	my ($self, $action, $constraint) = @_;

	# a super-user/super-role can do whatever they want
	return 1 if $self->is_super;

	# return false if user/role doesn't have that ability
	return unless $self->abilities->{$action};

	# user/role has ability, but is there a constraint?
	if ($constraint && $constraint ne '_all_') {
		# return true if user/role's ability is not constrained
		return 1 if !ref $self->abilities->{$action};
		
		# it is constrained (or at least it should be, let's make
		# sure we have an array-ref of constraints)
		if (ref $self->abilities->{$action} eq 'ARRAY') {
			return 1 if $constraint eq '_any_';	# caller wants to know if
								# user/role has any constraint,
								# which we now know is true
			foreach (@{$self->abilities->{$action}}) {