NAME

Catalyst::Manual::Tutorial::Authentication - Catalyst Tutorial - Chapter 5: Authentication

OVERVIEW

This is Chapter 5 of 10 for the Catalyst tutorial.

DESCRIPTION

Now that we finally have a simple yet functional application, we can focus on providing authentication (with authorization coming next in Chapter 6).

This chapter of the tutorial is divided into two main sections: 1) basic, cleartext authentication and 2) hash-based authentication.

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

BASIC AUTHENTICATION

This section explores how to add authentication logic to a Catalyst application.

Add Users and Roles to the Database

First, we add both user and role information to the database (we will add the role information here although it will not be used until the authorization section, Chapter 6). Create a new SQL script file by opening myapp02.sql in your editor and insert:

--
-- Add users and roles tables, along with a many-to-many join table
--
CREATE TABLE users (
        id            INTEGER PRIMARY KEY,
        username      TEXT,
        password      TEXT,
        email_address TEXT,
        first_name    TEXT,
        last_name     TEXT,
        active        INTEGER
);
CREATE TABLE roles (
        id   INTEGER PRIMARY KEY,
        role TEXT
);
CREATE TABLE user_roles (
        user_id INTEGER,
        role_id INTEGER,
        PRIMARY KEY (user_id, role_id)
);
--
-- Load up some initial test data
--
INSERT INTO users VALUES (1, 'test01', 'mypass', 't01@na.com', 'Joe',  'Blow', 1);
INSERT INTO users VALUES (2, 'test02', 'mypass', 't02@na.com', 'Jane', 'Doe',  1);
INSERT INTO users VALUES (3, 'test03', 'mypass', 't03@na.com', 'No',   'Go',   0);
INSERT INTO roles VALUES (1, 'user');
INSERT INTO roles VALUES (2, 'admin');
INSERT INTO user_roles VALUES (1, 1);
INSERT INTO user_roles VALUES (1, 2);
INSERT INTO user_roles VALUES (2, 1);
INSERT INTO user_roles VALUES (3, 1);

Then load this into the myapp.db database with the following command:

$ sqlite3 myapp.db < myapp02.sql

Add User and Role Information to DBIC Schema

Although we could manually edit the DBIC schema information to include the new tables added in the previous step, let's use the create=static option on the DBIC model helper to do most of the work for us:

$ script/myapp_create.pl model DB DBIC::Schema MyApp::Schema \
    create=static components=TimeStamp dbi:SQLite:myapp.db
 exists "/root/dev/MyApp/script/../lib/MyApp/Model"
 exists "/root/dev/MyApp/script/../t"
Dumping manual schema for MyApp::Schema to directory /root/dev/MyApp/script/../lib ...
Schema dump completed.
 exists "/root/dev/MyApp/script/../lib/MyApp/Model/DB.pm"
$
$ ls lib/MyApp/Schema/Result
Authors.pm  BookAuthors.pm  Books.pm  Roles.pm  UserRoles.pm  Users.pm

Notice how the helper has added three new table-specific result source files to the lib/MyApp/Schema/Result directory. And, more importantly, even if there were changes to the existing result source files, those changes would have only been written above the # DO NOT MODIFY THIS OR ANYTHING ABOVE! comment and your hand-edited enhancements would have been preserved.

Speaking of "hand-edit ted enhancements," we should now add relationship information to the three new result source files. Edit each of these files and add the following information between the # DO NOT MODIFY THIS OR ANYTHING ABOVE! comment and the closing 1;:

lib/MyApp/Schema/Result/Users.pm:

#
# Set relationships:
#

# has_many():
#   args:
#     1) Name of relationship, DBIC will create accessor with this name
#     2) Name of the model class referenced by this relationship
#     3) Column name in *foreign* table (aka, foreign key in peer table)
__PACKAGE__->has_many(map_user_role => 'MyApp::Schema::Result::UserRoles', 'user_id');

# many_to_many():
#   args:
#     1) Name of relationship, DBIC will create accessor with this name
#     2) Name of has_many() relationship this many_to_many() is shortcut for
#     3) Name of belongs_to() relationship in model class of has_many() above
#   You must already have the has_many() defined to use a many_to_many().
__PACKAGE__->many_to_many(roles => 'map_user_role', 'role');

lib/MyApp/Schema/Result/Roles.pm:

#
# Set relationships:
#

# has_many():
#   args:
#     1) Name of relationship, DBIC will create accessor with this name
#     2) Name of the model class referenced by this relationship
#     3) Column name in *foreign* table (aka, foreign key in peer table)
__PACKAGE__->has_many(map_user_role => 'MyApp::Schema::Result::UserRoles', 'role_id');

lib/MyApp/Schema/Result/UserRoles.pm:

#
# Set relationships:
#

# belongs_to():
#   args:
#     1) Name of relationship, DBIC will create accessor with this name
#     2) Name of the model class referenced by this relationship
#     3) Column name in *this* table
__PACKAGE__->belongs_to(user => 'MyApp::Schema::Result::Users', 'user_id');

# belongs_to():
#   args:
#     1) Name of relationship, DBIC will create accessor with this name
#     2) Name of the model class referenced by this relationship
#     3) Column name in *this* table
__PACKAGE__->belongs_to(role => 'MyApp::Schema::Result::Roles', 'role_id');

The code for these three sets of updates is obviously very similar to the edits we made to the Books, Authors, and BookAuthors classes created in Chapter 3.

Note that we do not need to make any change to the lib/MyApp/Schema.pm schema file. It simply tells DBIC to load all of the Result Class and ResultSet Class files it finds in below the lib/MyApp/Schema directory, so it will automatically pick up our new table information.

Sanity-Check Reload of Development Server

We aren't ready to try out the authentication just yet; we only want to do a quick check to be sure our model loads correctly. Press Ctrl-C to kill the previous server instance (if it's still running) and restart it:

$ script/myapp_server.pl

Look for the three new model objects in the startup debug output:

...
 .-------------------------------------------------------------------+----------.
| Class                                                             | Type     |
+-------------------------------------------------------------------+----------+
| MyApp::Controller::Books                                          | instance |
| MyApp::Controller::Root                                           | instance |
| MyApp::Model::DB                                                  | instance |
| MyApp::Model::DB::Author                                          | class    |
| MyApp::Model::DB::Books                                           | class    |
| MyApp::Model::DB::BookAuthors                                     | class    |
| MyApp::Model::DB::Roles                                           | class    |
| MyApp::Model::DB::Users                                           | class    |
| MyApp::Model::DB::UserRoles                                       | class    |
| MyApp::View::TT                                                   | instance |
'-------------------------------------------------------------------+----------'
...

Again, notice that your "Result Class" classes have been "re-loaded" by Catalyst under MyApp::Model.

Include Authentication and Session Plugins

Edit lib/MyApp.pm and update it as follows (everything below StackTrace is new):

# Load plugins
use Catalyst qw/-Debug
            ConfigLoader
            Static::Simple

            StackTrace

            Authentication

            Session
            Session::Store::FastMmap
            Session::State::Cookie
            /;

Note: As discussed in MoreCatalystBasics, different versions of Catalyst::Devel have used a variety of methods to load the plugins. You can put the plugins in the use Catalyst statement if you prefer.

The Authentication plugin supports Authentication while the Session plugins are required to maintain state across multiple HTTP requests.

Note that the only required Authentication class is the main one. This is a change that occurred in version 0.09999_01 of the Authentication plugin. You do not need to specify a particular Authentication::Store or Authentication::Credential plugin. Instead, indicate the Store and Credential you want to use in your application configuration (see below).

Note that there are several options for Session::Store (Session::Store::FastMmap is generally a good choice if you are on Unix; try Session::Store::File if you are on Win32) -- consult Session::Store and its subclasses for additional information and options (for example to use a database- backed session store).

Configure Authentication

Although __PACKAGE__->config(name => 'value'); is still supported, newer Catalyst applications tend to place all configuration information in myapp.conf and automatically load this information into MyApp->config using the ConfigLoader plugin.

As discussed in Chapter 3 of the tutorial, Catalyst has recently switched from a default config file format of YAML to Config::General (an apache-like format). In case you are using a version of Catalyst earlier than v5.7014, delete the myapp.yml, or convert it to .conf format using the TIP in "EDIT THE LIST OF CATALYST PLUGINS" in Catalyst::Manual::MoreCatalystBasics then simply follow the directions below to create a new myapp.conf file. Although we will use the Config::General format here because YAML files can be difficult to cut and paste in certain environments, you are free to use any format supported by Catalyst::Plugin::ConfigLoader and Config::Any -- Catalyst will transparently handle the different formats.

Here, we need to load several parameters that tell Catalyst::Plugin::Authentication where to locate information in your database. To do this, edit the myapp.conf file and update it to match:

# 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
                # We are using an unencrypted password for now
                password_type clear
            </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::Result::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
            </store>
        </dbic>
    </realms>
</authentication>

Inline comments in the code above explain how each field is being used.

Use the Catalyst create script to create two stub controller files:

$ script/myapp_create.pl controller Login
$ script/myapp_create.pl controller Logout

You could easily use a single controller here. For example, you could have a User controller with both login and logout actions. Remember, Catalyst is designed to be very flexible, and leaves such matters up to you, the designer and programmer.

Then open lib/MyApp/Controller/Login.pm, locate the sub index :Path :Args(0) method (or sub index : Private if you are using an older version of Catalyst) that was automatically inserted by the helpers when we created the Login controller above, and update the definition of sub index to match:

=head2 index

Login logic

=cut

sub index :Path :Args(0) {
    my ($self, $c) = @_;

    # Get the username and password from form
    my $username = $c->request->params->{username} || "";
    my $password = $c->request->params->{password} || "";

    # If the username and password values were found in form
    if ($username && $password) {
        # Attempt to log the user in
        if ($c->authenticate({ username => $username,
                               password => $password  } )) {
            # If successful, then let them use the application
            $c->response->redirect($c->uri_for(
                $c->controller('Books')->action_for('list')));
            return;
        } else {
            # Set an error message
            $c->stash->{error_msg} = "Bad username or password.";
        }
    }

    # If either of above don't work out, send to the login page
    $c->stash->{template} = 'login.tt2';
}

This controller fetches the username and password values from the login form and attempts to authenticate the user. If successful, it redirects the user to the book list page. If the login fails, the user will stay at the login page and receive an error message. If the username and password values are not present in the form, the user will be taken to the empty login form.

Note that we could have used something like "sub default :Path", however, it is generally recommended (partly for historical reasons, and partly for code clarity) only to use default in MyApp::Controller::Root, and then mainly to generate the 404 not found page for the application.

Instead, we are using "sub somename :Path :Args(0) {...}" here to specifically match the URL /login. Path actions (aka, "literal actions") create URI matches relative to the namespace of the controller where they are defined. Although Path supports arguments that allow relative and absolute paths to be defined, here we use an empty Path definition to match on just the name of the controller itself. The method name, index, is arbitrary. We make the match even more specific with the :Args(0) action modifier -- this forces the match on only /login, not /login/somethingelse.

Next, update the corresponding method in lib/MyApp/Controller/Logout.pm to match:

=head2 index

Logout logic

=cut

sub index :Path :Args(0) {
    my ($self, $c) = @_;

    # Clear the user's state
    $c->logout;

    # Send the user to the starting point
    $c->response->redirect($c->uri_for('/'));
}

As with the login controller, be sure to delete the $c->response->body('Matched MyApp::Controller::Logout in Logout.'); line of the sub index.

Create a login form by opening root/src/login.tt2 and inserting:

[% META title = 'Login' %]

<!-- Login form -->
<form method="post" action="[% c.uri_for('/login') %]">
  <table>
    <tr>
      <td>Username:</td>
      <td><input type="text" name="username" size="40" /></td>
    </tr>
    <tr>
      <td>Password:</td>
      <td><input type="password" name="password" size="40" /></td>
    </tr>
    <tr>
      <td colspan="2"><input type="submit" name="submit" value="Submit" /></td>
    </tr>
  </table>
</form>

Add Valid User Check

We need something that provides enforcement for the authentication mechanism -- a global mechanism that prevents users who have not passed authentication from reaching any pages except the login page. This is generally done via an auto action/method (prior to Catalyst v5.66, this sort of thing would go in MyApp.pm, but starting in v5.66, the preferred location is lib/MyApp/Controller/Root.pm).

Edit the existing lib/MyApp/Controller/Root.pm class file and insert the following method:

=head2 auto

Check if there is a user and, if not, forward to login page

=cut

# Note that 'auto' runs after 'begin' but before your actions and that
# 'auto's "chain" (all from application path to most specific class are run)
# See the 'Actions' section of 'Catalyst::Manual::Intro' for more info.
sub auto : Private {
    my ($self, $c) = @_;

    # Allow unauthenticated users to reach the login page.  This
    # allows unauthenticated users to reach any action in the Login
    # controller.  To lock it down to a single action, we could use:
    #   if ($c->action eq $c->controller('Login')->action_for('index'))
    # to only allow unauthenticated access to the 'index' action we
    # added above.
    if ($c->controller eq $c->controller('Login')) {
        return 1;
    }

    # If a user doesn't exist, force login
    if (!$c->user_exists) {
        # Dump a log message to the development server debug output
        $c->log->debug('***Root::auto User not found, forwarding to /login');
        # Redirect the user to the login page
        $c->response->redirect($c->uri_for('/login'));
        # Return 0 to cancel 'post-auto' processing and prevent use of application
        return 0;
    }

    # User found, so return 1 to continue with processing after this 'auto'
    return 1;
}

As discussed in "CREATE A CATALYST CONTROLLER" in Catalyst::Manual::Tutorial::MoreCatalystBasics, every auto method from the application/root controller down to the most specific controller will be called. By placing the authentication enforcement code inside the auto method of lib/MyApp/Controller/Root.pm (or lib/MyApp.pm), it will be called for every request that is received by the entire application.

Displaying Content Only to Authenticated Users

Let's say you want to provide some information on the login page that changes depending on whether the user has authenticated yet. To do this, open root/src/login.tt2 in your editor and add the following lines to the bottom of the file:

...
<p>
[%
   # This code illustrates how certain parts of the TT
   # template will only be shown to users who have logged in
%]
[% IF c.user_exists %]
    Please Note: You are already logged in as '[% c.user.username %]'.
    You can <a href="[% c.uri_for('/logout') %]">logout</a> here.
[% ELSE %]
    You need to log in to use this application.
[% END %]
[%#
   Note that this whole block is a comment because the "#" appears
   immediate after the "[%" (with no spaces in between).  Although it
   can be a handy way to temporarily "comment out" a whole block of
   TT code, it's probably a little too subtle for use in "normal"
   comments.
%]
</p>

Although most of the code is comments, the middle few lines provide a "you are already logged in" reminder if the user returns to the login page after they have already authenticated. For users who have not yet authenticated, a "You need to log in..." message is displayed (note the use of an IF-THEN-ELSE construct in TT).

Try Out Authentication

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

$ script/myapp_server.pl

IMPORTANT NOTE: If you are having issues with authentication on Internet Explorer, be sure to check the system clocks on both your server and client machines. Internet Explorer is very picky about timestamps for cookies. You can quickly sync a Debian system by installing the "ntpdate" package:

sudo aptitude -y install ntpdate

And then run the following command:

sudo ntpdate-debian

Or, depending on your firewall configuration:

sudo ntpdate-debian -u

Note: NTP can be a little more finicky about firewalls because it uses UDP vs. the more common TCP that you see with most Internet protocols. Worse case, you might have to manually set the time on your development box instead of using NTP.

Now trying going to http://localhost:3000/books/list and you should be redirected to the login page, hitting Shift+Reload or Ctrl+Reload if necessary (the "You are already logged in" message should not appear -- if it does, click the logout button and try again). Note the ***Root::auto User not found... debug message in the development server output. Enter username test01 and password mypass, and you should be taken to the Book List page.

Open root/src/books/list.tt2 and add the following lines to the bottom (below the closing </table> tag):

<p>
  <a href="[% c.uri_for('/login') %]">Login</a>
  <a href="[% c.uri_for(c.controller.action_for('form_create')) %]">Create</a>
</p>

Reload your browser and you should now see a "Login" and "Create" links at the bottom of the page (as mentioned earlier, you can update template files without reloading the development server). Click the first link to return to the login page. This time you should see the "You are already logged in" message.

Finally, click the You can logout here link on the /login page. You should stay at the login page, but the message should change to "You need to log in to use this application."

USING PASSWORD HASHES

In this section we increase the security of our system by converting from cleartext passwords to SHA-1 password hashes.

Note: This section is optional. You can skip it and the rest of the tutorial will function normally.

Be aware that even with the techniques shown in this section, the browser still transmits the passwords in cleartext to your application. We are just avoiding the storage of cleartext passwords in the database by using a SHA-1 hash. If you are concerned about cleartext passwords between the browser and your application, consider using SSL/TLS, made easy with the Catalyst plugin Catalyst::Plugin:RequireSSL. You should also consider adding a "salt" mechanism to your hashed passwords to mitigate the risk of a "rainbow table" crack against your passwords (see Catalyst::Authentication::Credential::Password for more information on using a salt value).

Get a SHA-1 Hash for the Password

Catalyst uses the Digest module to support a variety of hashing algorithms. Here we will use SHA-1 (SHA = Secure Hash Algorithm). First, we should compute the SHA-1 hash for the "mypass" password we are using. The following command-line Perl script provides a "quick and dirty" way to do this:

$ perl -MDigest::SHA -e 'print Digest::SHA::sha1_hex("mypass"), "\n"'
e727d1464ae12436e899a726da5b2f11d8381b26

Note: You should probably modify this code for production use to not read the password from the command line. By having the script prompt for the cleartext password, it avoids having the password linger in forms such as your .bash_history files (assuming you are using BASH as your shell). An example of such a script can be found in Appendix 3.

Switch to SHA-1 Password Hashes in the Database

Next, we need to change the password column of our users table to store this hash value vs. the existing cleartext password. Open myapp03.sql in your editor and enter:

--
-- Convert passwords to SHA-1 hashes
--
UPDATE users SET password = 'e727d1464ae12436e899a726da5b2f11d8381b26' WHERE id = 1;
UPDATE users SET password = 'e727d1464ae12436e899a726da5b2f11d8381b26' WHERE id = 2;
UPDATE users SET password = 'e727d1464ae12436e899a726da5b2f11d8381b26' WHERE id = 3;

Then use the following command to update the SQLite database:

$ sqlite3 myapp.db < myapp03.sql

Note: We are using SHA-1 hashes here, but many other hashing algorithms are supported. See Digest for more information.

Enable SHA-1 Hash Passwords in `Catalyst::Plugin::Authentication::Store::DBIC`

Edit myapp.conf and update it to match (the password_type and password_hash_type are new, everything else is the same):

# 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::Result::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
            </store>
        </dbic>
    </realms>
</authentication>

Try Out the Hashed Passwords

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

$ script/myapp_server.pl

You should now be able to go to http://localhost:3000/books/list and login as before. When done, click the "logout" link on the login page (or point your browser at http://localhost:3000/logout).

USING THE SESSION FOR FLASH

As discussed in the previous chapter of the tutorial, flash allows you to set variables in a way that is very similar to stash, but it will remain set across multiple requests. Once the value is read, it is cleared (unless reset). Although flash has nothing to do with authentication, it does leverage the same session plugins. Now that those plugins are enabled, let's go back and update the "delete and redirect with query parameters" code seen at the end of the Basic CRUD chapter of the tutorial to take advantage of flash.

First, open lib/MyApp/Controller/Books.pm and modify sub delete to match the following (everything after the model search line of code has changed):

=head2 delete

Delete a book

=cut

sub delete :Chained('object') :PathPart('delete') :Args(0) {
    my ($self, $c) = @_;

    # Use the book object saved by 'object' and delete it along
    # with related 'book_authors' entries
    $c->stash->{object}->delete;

    # Use 'flash' to save information across requests until it's read
    $c->flash->{status_msg} = "Book deleted";

    # Redirect the user back to the list page
    $c->response->redirect($c->uri_for($self->action_for('list')));
}

Next, open root/src/wrapper.tt2 and update the TT code to pull from flash vs. the status_msg query parameter:

...
<div id="content">
    [%# Status and error messages %]
    <span class="message">[% status_msg || c.flash.status_msg %]</span>
    <span class="error">[% error_msg %]</span>
    [%# This is where TT will stick all of your template's contents. -%]
    [% content %]
</div><!-- end content -->
...

Although the sample above only shows the content div, leave the rest of the file intact -- the only change we made to the wrapper.tt2 was to add "|| c.request.params.status_msg" to the <span class="message"> line.

Try Out Flash

Restart the development server, log in, and then point your browser to http://localhost:3000/books/url_create/Test/1/4 to create an extra several books. Click the "Return to list" link and delete one of the "Test" books you just added. The flash mechanism should retain our "Book deleted" status message across the redirect.

NOTE: While flash will save information across multiple requests, it does get cleared the first time it is read. In general, this is exactly what you want -- the flash message will get displayed on the next screen where it's appropriate, but it won't "keep showing up" after that first time (unless you reset it). Please refer to Catalyst::Plugin::Session for additional information.

Switch To Flash-To-Stash

Although the a use of flash above works well, the status_msg || c.flash.status_msg statement is a little ugly. A nice alternative is to use the flash_to_stash feature that automatically copies the content of flash to stash. This makes your controller and template code work regardless of where it was directly access, a forward, or a redirect. To enable flash_to_stash, you can either set the value in lib/MyApp.pm by changing the default __PACKAGE__->config setting to something like:

__PACKAGE__->config(
        name => 'MyApp',
        session => {flash_to_stash => 1}
    );

or add the following to myapp.conf:

<session>
    flash_to_stash   1
</session>

The __PACKAGE__->config option is probably preferable here since it's not something you will want to change at runtime without it possibly breaking some of your code.

Then edit root/src/wrapper.tt2 and change the status_msg line to match the following:

<span class="message">[% status_msg %]</span>

Restart the development server and go to http://localhost:3000/books/list in your browser. Delete another of the "Test" books you added in the previous step. Flash should still maintain the status message across the redirect even though you are no longer explicitly accessing c.flash.

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/Catalyst-Manual/5.70/trunk/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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