NAME

Catalyst::Manual::Tutorial::Authorization - Catalyst Tutorial - Part 5: Authorization

OVERVIEW

This is Part 5 of 9 for the Catalyst tutorial.

DESCRIPTION

This part of the tutorial adds role-based authorization to the existing authentication implemented in Part 4. It provides simple examples of how to use roles in both TT templates and controller actions. The first half looks at manually configured authorization. The second half looks at how the ACL authorization plugin can simplify your code.

You can checkout the source code for this example from the catalyst subversion repository as per the instructions in Catalyst::Manual::Tutorial::Intro

BASIC AUTHORIZATION

In this section you learn how to manually configure authorization.

Update Plugins to Include Support for Authorization

Edit lib/MyApp.pm and add Authorization::Roles to the list:

use Catalyst qw/
        -Debug
        ConfigLoader
        Static::Simple
        
        StackTrace
        
        Authentication
        Authentication::Store::DBIC
        Authentication::Credential::Password
        Authorization::Roles
        
        Session
        Session::Store::FastMmap
        Session::State::Cookie
        /;

Add Config Information for Authorization

Edit myapp.yml and update it to match (everything from the "authorization:" line down is new):

---
name: MyApp
authentication:
    dbic:
        # Note this first definition would be the same as setting
        # __PACKAGE__->config->{authentication}->{dbic}->{user_class} = 'MyAppDB::User'
        # in lib/MyApp.pm (IOW, each hash key becomes a "name:" in the YAML file).
        #
        # This is the model object created by Catalyst::Model::DBIC from your
        # schema (you created 'MyAppDB::User' but as the Catalyst startup
        # debug messages show, it was loaded as 'MyApp::Model::MyAppDB::User').
        # NOTE: Omit 'MyApp::Model' here just as you would when using 
        # '$c->model("MyAppDB::User)'
        user_class: MyAppDB::User
        # This is the name of the field in your 'users' table that contains the user's name
        user_field: username
        # This is the name of the field in your 'users' table that contains the password
        password_field: password
        # Other options can go here for hashed passwords
        # Enabled hashed passwords
        password_type: hashed
        # Use the SHA-1 hashing algorithm
        password_hash_type: SHA-1
authorization:
    dbic:
        # This is the model object created by Catalyst::Model::DBIC from your
        # schema (you created 'MyAppDB::Role' but as the Catalyst startup
        # debug messages show, it was loaded as 'MyApp::Model::MyAppDB::Role').
        # NOTE: Omit 'MyApp::Model' here just as you would when using 
        # '$c->model("MyAppDB::User)'
        role_class: MyAppDB::Role
        # The name of the field in the 'roles' table that contains the role name
        role_field: role
        # The name of the accessor used to map a role to the users who have this role
        # See the has_many() in MyAppDB/Role.pm
        role_rel: map_user_role
        # The name of the field in the user_role table that references the user
        user_role_user_field: user_id

Add Role-Specific Logic to the "Book List" Template

Open root/src/books/list.tt2 in your editor and add the following lines to the bottom of the file:

<p>Hello [% Catalyst.user.username %], you have the following roles:</p>

<ul>
  [% # Dump list of roles -%]
  [% FOR role = Catalyst.user.roles %]<li>[% role %]</li>[% END %]
</ul>

<p>
[% # Add some simple role-specific logic to template %]
[% # Use $c->check_user_roles() to check authz -%]
[% IF Catalyst.check_user_roles('user') %]
  [% # Give normal users a link for 'logout' %]
  <a href="[% Catalyst.uri_for('/logout') %]">Logout</a>
[% END %]

[% # Can also use $c->user->check_roles() to check authz -%]
[% IF Catalyst.check_user_roles('admin') %]
  [% # Give admin users a link for 'create' %]
  <a href="[% Catalyst.uri_for('form_create') %]">Create</a>
[% END %]
</p>

This code displays a different combination of links depending on the roles assigned to the user.

Limit `Books::add` to `admin` Users

IF statements in TT templates simply control the output that is sent to the user's browser; it provides no real enforcement (if users know or guess the appropriate URLs, they are still perfectly free to hit any action within your application). We need to enhance the controller logic to wrap restricted actions with role-validation logic.

For example, we might want to restrict the "formless create" action to admin-level users by editing lib/MyApp/Controller/Books.pm and updating url_create to match the following code:

=head2 url_create

Create a book with the supplied title and rating,
with manual authorization

=cut

sub url_create : Local {
    # In addition to self & context, get the title, rating & author_id args
    # from the URL.  Note that Catalyst automatically puts extra information
    # after the "/<controller_name>/<action_name/" into @_
    my ($self, $c, $title, $rating, $author_id) = @_;

    # Check the user's roles
    if ($c->check_user_roles('admin')) {
        # Call create() on the book model object. Pass the table 
        # columns/field values we want to set as hash values
        my $book = $c->model('MyAppDB::Book')->create({
                title   => $title,
                rating  => $rating
            });
        
        # Add a record to the join table for this book, mapping to 
        # appropriate author
        $book->add_to_book_authors({author_id => $author_id});
        # Note: Above is a shortcut for this:
        # $book->create_related('book_authors', {author_id => $author_id});
        
        # Assign the Book object to the stash for display in the view
        $c->stash->{book} = $book;
    
        # This is a hack to disable XSUB processing in Data::Dumper
        # (it's used in the view).  This is a work-around for a bug in
        # the interaction of some versions or Perl, Data::Dumper & DBIC.
        # You won't need this if you aren't using Data::Dumper (or if
        # you are running DBIC 0.06001 or greater), but adding it doesn't 
        # hurt anything either.
        $Data::Dumper::Useperl = 1;
    
        # Set the TT template to use
        $c->stash->{template} = 'books/create_done.tt2';
    } else {
        # Provide very simple feedback to the user
        $c->response->body('Unauthorized!');
    }
}

To add authorization, we simply wrap the main code of this method in an if statement that calls check_user_roles. If the user does not have the appropriate permissions, they receive an "Unauthorized!" message. Note that we intentionally chose to display the message this way to demonstrate that TT templates will not be used if the response body has already been set. In reality you would probably want to use a technique that maintains the visual continuity of your template layout (for example, using the "status" or "error" message feature added in Part 2).

TIP: If you want to keep your existing url_create method, you can create a new copy and comment out the original by making it look like a Pod comment. For example, put something like =begin before sub add : Local { and =end after the closing }.

Try Out Authentication And Authorization

Press Ctrl-C to kill the previous server instance (if it's still running) and restart it:

$ script/myapp_server.pl

Now trying going to http://localhost:3000/books/list and you should be taken to the login page (you might have to Shift+Reload your browser and/or click the "Logout" link on the book list page). Try logging in with both test01 and test02 (both use a password of mypass) and notice how the roles information updates at the bottom of the "Book List" page. Also try the Logout link on the book list page.

Now the "url_create" URL will work if you are already logged in as user test01, but receive an authorization failure if you are logged in as test02. Try:

http://localhost:3000/books/url_create/test/1/6

while logged in as each user. Use one of the 'Logout' links (or go to http://localhost:3000/logout in you browser directly) when you are done.

ENABLE ACL-BASED AUTHORIZATION

This section takes a brief look at how the Catalyst::Plugin::Authorization::ACL plugin can automate much of the work required to perform role-based authorization in a Catalyst application.

Add the `Catalyst::Plugin::Authorization::ACL` Plugin

Open lib/MyApp.pm in your editor and add the following plugin to the use Catalyst statement:

Authorization::ACL

Note that the remaining use Catalyst plugins from earlier sections are not shown here, but they should still be included.

Add ACL Rules to the Application Class

Open lib/MyApp.pm in your editor and add the following BELOW the __PACKAGE__->setup; statement:

# Authorization::ACL Rules
__PACKAGE__->deny_access_unless(
        "/books/form_create",
        [qw/admin/],
    );
__PACKAGE__->deny_access_unless(
        "/books/form_create_do",
        [qw/admin/],
    );
__PACKAGE__->deny_access_unless(
        "/books/delete",
        [qw/user admin/],
    );

Each of the three statements above comprises an ACL plugin "rule". The first two rules only allow admin-level users to create new books using the form (both the form itself and the data submission logic are protected). The third statement allows both users and admins to delete books. The /books/url_create action will continue to be protected by the "manually configured" authorization created earlier in this part of the tutorial.

The ACL plugin permits you to apply allow/deny logic in a variety of ways. The following provides a basic overview of the capabilities:

The ACL plugin only operates on the Catalyst "private namespace". You are using the private namespace when you use Local actions. Path, Regex, and Global allow you to specify actions where the path and the namespace differ -- the ACL plugin will not work in these cases.
Each rule is expressed in a separate __PACKAGE__->deny_access_unless() or __PACKAGE__->allow_access_if() line (there are several other methods that can be used for more complex policies, see the METHODS portion of the Catalyst::Plugin::Authorization::ACL documentation for more details).
Each rule can contain multiple roles but only a single path.
The rules are tried in order (with the "most specific" rules tested first), and processing stops at the first "match" where an allow or deny is specified. Rules "fall through" if there is not a "match" (where a "match" means the user has the specified role). If a "match" is found, then processing stops there and the appropriate allow/deny action is taken.
If none of the rules match, then access is allowed.
The rules currently need to be specific in the application class lib\MyApp.pm after the __PACKAGE__->setup; line.

Add a Method to Handle Access Violations

By default, Catalyst::Plugin::Authorization::ACL throws an exception when authorization fails. This will take the user to the Catalyst debug screen, or a "Please come back later" message if you are not using the -Debug flag. This step uses the access_denied method in order to provide more appropriate feedback to the user.

Open lib/MyApp/Controller/Books.pm in your editor and add the following method:

=head2 access_denied

Handle Catalyst::Plugin::Authorization::ACL access denied exceptions

=cut

sub access_denied : Private {
    my ($self, $c) = @_;

    # Set the error message
    $c->stash->{error_msg} = 'Unauthorized!';

    # Display the list
    $c->forward('list');
}

Then run the Catalyst development server script:

$ script/myapp_server.pl

Log in as test02. Once at the book list, click the "Create" link to try the form_create action. You should receive a red "Unauthorized!" error message at the top of the list. (Note that in reality you would probably want to place the "Create" link code in root/src/books/list.tt2 inside an IF statement that only displays the list to admin-level users.) If you log in as test01 you should be able to view the form_create form and add a new book.

When you are done, use one of the 'Logout' links (or go to the http://localhost:3000/logout URL directly) when you are done.

AUTHOR

Kennedy Clark, hkclark@gmail.com

Please report any errors, issues or suggestions to the author. The most recent version of the Catalyst Tutorial can be found at http://dev.catalyst.perl.org/repos/Catalyst/trunk/Catalyst-Manual/lib/Catalyst/Manual/Tutorial/.

To install Catalyst::Manual, copy and paste the appropriate command in to your terminal.

cpanm

cpanm Catalyst::Manual

CPAN shell

perl -MCPAN -e shell
install Catalyst::Manual

For more information on module installation, please visit the detailed CPAN module installation guide.

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