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עידו פרלמוטר (Ido Perlmuter) > Abilities-0.5 > Abilities



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Module Version: 0.5   Source  


Abilities - Simple, hierarchical user authorization for web applications, with optional support for plan-based (paid) services.


version 0.5


        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 ($user->can_perform('something')) {
        } else {
                die "Hey you can't do that, you can only do " . join(', ', keys %{$user->abilities});


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 Catalyst (See Catalyst::Plugin::Authorization::Roles for the role-based implementation and 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 Abilities module is implemented as a Moo role (which makes it compatible with 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. Entities is a reference implementation that can be used by applications, or just taken as an example of an ability-based authorization system. Entities::User and Entities::Role are the user and role classes that consume the Abilities role in the Entities distribution.


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. 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 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 Abilities module.


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 Abilities::Features module provided with this distribution. Read its documentation for detailed information.


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


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.


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.


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.

get_role( $name )

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


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

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.

assigned_role( $role_name )

This method receives a role name and returns a true value if the user/role is a direct member of the provided role. Only direct membership is checked, so the user/role must be specifically assigned to the provided role, and not to a role that inherits from that role (see "does_role( $role )" instead).

does_role( $role_name )

Receives the name of a role, and returns a true value if the user/role inherits the abilities of the provided role. This method takes inheritance into account, so if a user was directly assigned to the 'admins' role, and the 'admins' role inherits from the 'devs' role, then does_role('devs') will return true for that user (while assigned_role('devs') returns false).


Returns a hash reference of all the abilities a user/role object can perform, after consolidating abilities inherited from roles (including recursively) and directly granted. Keys in the hash-ref will be names of actions, values will be 1 (for yes/no actions) or a single-item array-ref with the name of a constraint (for constrained actions).


Up to version 0.2, Abilities required the roles and actions attributes to return objects. While this made it easier to calculate abilities, it made this system a bit less flexible.

In version 0.3, Abilities changed the requirement such that both these attributes need to return strings (the names of the roles/actions). If your implementation has granted roles and actions stored in a database by names, this made life a bit easier for you. On other implementations, however, this has the potential of requiring you to write a bit more code. If that is the case, I apologize, but keep in mind that you can still store granted roles and actions any way you want in a database (either by names or by references), just as long as you correctly provide roles and actions.

Unfortunately, in both versions 0.3 and 0.4, I made a bit of a mess that rendered both versions unusable. While I documented the roles attribute as requiring role names instead of role objects, the actual implementation still required role objects. This has now been fixed, but it also meant I had to add a new requirement: consuming classes now have to provide a method called get_role() that takes the name of a role and returns its object. This will probably means loading the role from a database and blessing it into your role class that also consumes this module.

I apologize for any inconvenience this might have caused.


Ido Perlmuter, <ido at ido50 dot net>


Please report any bugs or feature requests to bug-abilities at, or through the web interface at I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.


You can find documentation for this module with the perldoc command.

        perldoc Abilities

You can also look for information at:


Copyright 2010-2013 Ido Perlmuter.

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.

See for more information.

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