=head1 NAME

Catalyst::Manual::Tutorial::Authorization - Catalyst Tutorial - Part 6: Authorization


=head1 OVERVIEW

This is B<Part 6 of 10> for the Catalyst tutorial.

L<Tutorial Overview|Catalyst::Manual::Tutorial>

=over 4

=item 1

L<Introduction|Catalyst::Manual::Tutorial::Intro>

=item 2

L<Catalyst Basics|Catalyst::Manual::Tutorial::CatalystBasics>

=item 3

L<More Catalyst Basics|Catalyst::Manual::Tutorial::MoreCatalystBasics>

=item 4

L<Basic CRUD|Catalyst::Manual::Tutorial::BasicCRUD>

=item 5

L<Authentication|Catalyst::Manual::Tutorial::Authentication>

=item 6

B<Authorization>

=item 7

L<Debugging|Catalyst::Manual::Tutorial::Debugging>

=item 8

L<Testing|Catalyst::Manual::Tutorial::Testing>

=item 9

L<Advanced CRUD|Catalyst::Manual::Tutorial::AdvancedCRUD>

=item 10

L<Appendices|Catalyst::Manual::Tutorial::Appendices>

=back


=head1 DESCRIPTION

This part of the tutorial adds role-based authorization to the existing
authentication implemented in Part 5.  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
L<Catalyst::Manual::Tutorial::Intro|Catalyst::Manual::Tutorial::Intro>.


=head1 BASIC AUTHORIZATION

In this section you learn how to manually configure authorization.


=head2 Update Plugins to Include Support for Authorization

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

    __PACKAGE__->setup(qw/
            -Debug
            ConfigLoader
            Static::Simple
    
            StackTrace
    
            Authentication
            Authorization::Roles
    
            Session
            Session::Store::FastMmap
            Session::State::Cookie
        /;


=head2 Add Config Information for Authorization

Edit C<myapp.conf> and update it to match the following (the
C<role_relation> and C<role_field> definitions are new):

    # rename this file to MyApp.yml and put a : in front of "name" if
    # you want to use yaml like in old versions of Catalyst
    name MyApp
    <authentication>
        default_realm dbic
        <realms>
            <dbic>
                <credential>
                    # Note this first definition would be the same as setting
                    # __PACKAGE__->config->{authentication}->{realms}->{dbic}
                    #     ->{credential} = 'Password' in lib/MyApp.pm
                    #
                    # Specify that we are going to do password-based auth
                    class Password
                    # This is the name of the field in the users table with the
                    # password stored in it
                    password_field password
                    # Switch to more secure hashed passwords
                    password_type  hashed
                    # Use the SHA-1 hashing algorithm
                    password_hash_type SHA-1
                </credential>
                <store>
                    # Use DBIC to retrieve username, password & role information
                    class DBIx::Class
                    # This is the model object created by Catalyst::Model::DBIC
                    # from your schema (you created 'MyApp::Schema::User' but as
                    # the Catalyst startup debug messages show, it was loaded as
                    # 'MyApp::Model::DB::Users').
                    # NOTE: Omit 'MyApp::Model' here just as you would when using
                    # '$c->model("DB::Users)'
                    user_class DB::Users
                    # This is the name of a many_to_many relation in the users
                    # object that points to the roles for that user
                    role_relation  roles
                    # This is the name of field in the roles table that contains
                    # the role information
                    role_field role
                </store>
            </dbic>
        </realms>
    </authentication>


=head2 Add Role-Specific Logic to the "Book List" Template

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

    <p>Hello [% c.user.username %], you have the following roles:</p>
    
    <ul>
      [% # Dump list of roles -%]
      [% FOR role = c.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 c.check_user_roles('user') %]
      [% # Give normal users a link for 'logout' %]
      <a href="[% c.uri_for('/logout') %]">Logout</a>
    [% END %]
    
    [% # Can also use $c->user->check_roles() to check authz -%]
    [% IF c.check_user_roles('admin') %]
      [% # Give admin users a link for 'create' %]
      <a href="[% c.uri_for('form_create') %]">Create</a>
    [% END %]
    </p>

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


=head2 Limit C<Books::add> to C<admin> Users

C<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 C<lib/MyApp/Controller/Books.pm> and
updating C<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('DB::Books')->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
C<if> statement that calls C<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 3).

B<TIP>: If you want to keep your existing C<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 C<=begin> before C<sub add
: Local {> and C<=end> after the closing C<}>.


=head2 Try Out Authentication And Authorization

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

    $ script/myapp_server.pl

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

Now the "url_create" URL will work if you are already logged in as user
C<test01>, but receive an authorization failure if you are logged in as
C<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 
L<http://localhost:3000/logout> in your browser directly) when you are 
done.


=head1 ENABLE ACL-BASED AUTHORIZATION

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


=head2 Add the C<Catalyst::Plugin::Authorization::ACL> Plugin

Open C<lib/MyApp.pm> in your editor and add the following plugin to the
C<__PACKAGE__-E<gt>setup> statement:

    Authorization::ACL

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


=head2 Add ACL Rules to the Application Class

Open C<lib/MyApp.pm> in your editor and add the following B<BELOW> the
C<__PACKAGE__-E<gt>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 C</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:

=over 4

=item *

The ACL plugin only operates on the Catalyst "private namespace".  You
are using the private namespace when you use C<Local> actions.  C<Path>,
C<Regex>, and C<Global> allow you to specify actions where the path and
the namespace differ -- the ACL plugin will not work in these cases.

=item *

Each rule is expressed in a separate
C<__PACKAGE__-E<gt>deny_access_unless()> or
C<__PACKAGE__-E<gt>allow_access_if()> line (there are several other
methods that can be used for more complex policies, see the C<METHODS>
portion of the
L<Catalyst::Plugin::Authorization::ACL|Catalyst::Plugin::Authorization::ACL>
documentation for more details).

=item *

Each rule can contain multiple roles but only a single path.

=item *

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.

=item *

If none of the rules match, then access is allowed.

=item *

The rules currently need to be specified in the application class
C<lib\MyApp.pm> B<after> the C<__PACKAGE__-E<gt>setup;> line.

=back


=head2 Add a Method to Handle Access Violations

By default,
L<Catalyst::Plugin::Authorization::ACL|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 C<-Debug> flag. This step uses the
C<access_denied> method in order to provide more appropriate feedback to
the user.

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

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


=head1 AUTHOR

Kennedy Clark, C<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
L<http://dev.catalyst.perl.org/repos/Catalyst/Catalyst-Manual/5.70/trunk/lib/Catalyst/Manual/Tutorial/>.

Copyright 2006-2008, Kennedy Clark, under Creative Commons License
(L<http://creativecommons.org/licenses/by-sa/3.0/us/>).

