Catalyst::Plugin::Session(3) ties together server side storage and client side state required to maintain session data.

SYNOPSIS


# To get sessions to "just work", all you need to do is use these plugins:
use Catalyst qw/
Session
Session::Store::FastMmap
Session::State::Cookie
/;
# you can replace Store::FastMmap with Store::File - both have sensible
# default configurations (see their docs for details)
# more complicated backends are available for other scenarios (DBI storage,
# etc)
# after you've loaded the plugins you can save session data
# For example, if you are writing a shopping cart, it could be implemented
# like this:
sub add_item : Local {
my ( $self, $c ) = @_;
my $item_id = $c->req->param("item");
# $c->session is a hash ref, a bit like $c->stash
# the difference is that it' preserved across requests
push @{ $c->session->{items} }, $item_id;
$c->forward("MyView");
}
sub display_items : Local {
my ( $self, $c ) = @_;
# values in $c->session are restored
$c->stash->{items_to_display} =
[ map { MyModel->retrieve($_) } @{ $c->session->{items} } ];
$c->forward("MyView");
}

DESCRIPTION

The Session plugin is the base of two related parts of functionality required for session management in web applications.

The first part, the State, is getting the browser to repeat back a session key, so that the web application can identify the client and logically string several requests together into a session.

The second part, the Store, deals with the actual storage of information about the client. This data is stored so that the it may be revived for every request made by the same client.

This plugin links the two pieces together.

RECOMENDED BACKENDS

Session::State::Cookie
The only really sane way to do state is using cookies.
Session::Store::File
A portable backend, based on Cache::File.
Session::Store::FastMmap
A fast and flexible backend, based on Cache::FastMmap.

METHODS

sessionid
An accessor for the session ID value.
session
Returns a hash reference that might contain unserialized values from previous requests in the same session, and whose modified value will be saved for future requests.

This method will automatically create a new session and session ID if none exists.

You can also set session keys by passing a list of key/value pairs or a hashref. 

    $c->session->{foo} = "bar";      # This works.
    $c->session(one => 1, two => 2); # And this.
    $c->session({ answer => 42 });   # And this.
session_expires
This method returns the time when the current session will expire, or 0 if there is no current session. If there is a session and it already expired, it will delete the session and return 0 as well.
flash
This is like Ruby on Rails' flash data structure. Think of it as a stash that lasts for longer than one request, letting you redirect instead of forward.

The flash data will be cleaned up only on requests on which actually use $c->flash (thus allowing multiple redirections), and the policy is to delete all the keys which haven't changed since the flash data was loaded at the end of every request.

Note that use of the flash is an easy way to get data across requests, but it's also strongly disrecommended, due it it being inherently plagued with race conditions. This means that it's unlikely to work well if your users have multiple tabs open at once, or if your site does a lot of AJAX requests.

Catalyst::Plugin::StatusMessage is the recommended alternative solution, as this doesn't suffer from these issues. 

    sub moose : Local {
        my ( $self, $c ) = @_;
        $c->flash->{beans} = 10;
        $c->response->redirect( $c->uri_for("foo") );
    }
    sub foo : Local {
        my ( $self, $c ) = @_;
        my $value = $c->flash->{beans};
        # ...
        $c->response->redirect( $c->uri_for("bar") );
    }
    sub bar : Local {
        my ( $self, $c ) = @_;
        if ( exists $c->flash->{beans} ) { # false
        }
    }
clear_flash
Zap all the keys in the flash regardless of their current state.
keep_flash @keys
If you want to keep a flash key for the next request too, even if it hasn't changed, call "keep_flash" and pass in the keys as arguments.
delete_session REASON
This method is used to invalidate a session. It takes an optional parameter which will be saved in "session_delete_reason" if provided.

NOTE: This method will also delete your flash data.

session_delete_reason
This accessor contains a string with the reason a session was deleted. Possible values include:
  • "address mismatch"
  • "session expired"
session_expire_key $key, $ttl
Mark a key to expire at a certain time (only useful when shorter than the expiry time for the whole session).

For example: 

    __PACKAGE__->config('Plugin::Session' => { expires => 10000000000 }); # "forever"
    (NB If this number is too large, Y2K38 breakage could result.)
    # later
    $c->session_expire_key( __user => 3600 );

Will make the session data survive, but the user will still be logged out after an hour.

Note that these values are not auto extended.

change_session_id
By calling this method you can force a session id change while keeping all session data. This method might come handy when you are paranoid about some advanced variations of session fixation attack.

If you want to prevent this session fixation scenario: 

    0) let us have WebApp with anonymous and authenticated parts
    1) a hacker goes to vulnerable WebApp and gets a real sessionid,
       just by browsing anonymous part of WebApp
    2) the hacker inserts (somehow) this values into a cookie in victim's browser
    3) after the victim logs into WebApp the hacker can enter his/her session

you should call change_session_id in your login controller like this: 

      if ($c->authenticate( { username => $user, password => $pass } )) {
        # login OK
        $c->change_session_id;
        ...
      } else {
        # login FAILED
        ...
      }
change_session_expires $expires
You can change the session expiration time for this session; 

    $c->change_session_expires( 4000 );

Note that this only works to set the session longer than the config setting.

INTERNAL METHODS

setup
This method is extended to also make calls to "check_session_plugin_requirements" and "setup_session".
check_session_plugin_requirements
This method ensures that a State and a Store plugin are also in use by the application.
setup_session
This method populates "$c->config('Plugin::Session')" with the default values listed in ``CONFIGURATION''.
prepare_action
This method is extended.

Its only effect is if the (off by default) "flash_to_stash" configuration parameter is on - then it will copy the contents of the flash to the stash at prepare time.

finalize_headers
This method is extended and will extend the expiry time before sending the response.
finalize_body
This method is extended and will call finalize_session before the other finalize_body methods run. Here we persist the session data if a session exists.
initialize_session_data
This method will initialize the internal structure of the session, and is called by the "session" method if appropriate.
create_session_id
Creates a new session ID using "generate_session_id" if there is no session ID yet.
validate_session_id SID
Make sure a session ID is of the right format.

This currently ensures that the session ID string is any amount of case insensitive hexadecimal characters.

generate_session_id
This method will return a string that can be used as a session ID. It is supposed to be a reasonably random string with enough bits to prevent collision. It basically takes "session_hash_seed" and hashes it using SHA-1, MD5 or SHA-256, depending on the availability of these modules.
session_hash_seed
This method is actually rather internal to generate_session_id, but should be overridable in case you want to provide more random data.

Currently it returns a concatenated string which contains:

  • A counter
  • The current time
  • One value from "rand".
  • The stringified value of a newly allocated hash reference
  • The stringified value of the Catalyst context object

in the hopes that those combined values are entropic enough for most uses. If this is not the case you can replace "session_hash_seed" with e.g. 

    sub session_hash_seed {
        open my $fh, "<", "/dev/random";
        read $fh, my $bytes, 20;
        close $fh;
        return $bytes;
    }

Or even more directly, replace "generate_session_id": 

    sub generate_session_id {
        open my $fh, "<", "/dev/random";
        read $fh, my $bytes, 20;
        close $fh;
        return unpack("H*", $bytes);
    }

Also have a look at Crypt::Random and the various openssl bindings - these modules provide APIs for cryptographically secure random data.

finalize_session
Clean up the session during "finalize".

This clears the various accessors after saving to the store.

dump_these
See ``dump_these'' in Catalyst - ammends the session data structure to the list of dumped objects if session ID is defined.
calculate_extended_session_expires
calculate_initial_session_expires
create_session_id_if_needed
delete_session_id
extend_session_expires
Note: this is *not* used to give an individual user a longer session. See 'change_session_expires'.
extend_session_id
get_session_id
reset_session_expires
session_is_valid
set_session_id
initial_session_expires

USING SESSIONS DURING PREPARE

The earliest point in time at which you may use the session data is after Catalyst::Plugin::Session's "prepare_action" has finished.

State plugins must set $c->session ID before "prepare_action", and during "prepare_action" Catalyst::Plugin::Session will actually load the data from the store. 

    sub prepare_action {
        my $c = shift;
        # don't touch $c->session yet!
        $c->NEXT::prepare_action( @_ );
        $c->session;  # this is OK
        $c->sessionid; # this is also OK
    }

CONFIGURATION

    $c->config('Plugin::Session' => {
        expires => 1234,
    });

All configuation parameters are provided in a hash reference under the "Plugin::Session" key in the configuration hash.

expires
The time-to-live of each session, expressed in seconds. Defaults to 7200 (two hours).
expiry_threshold
Only update the session expiry time if it would otherwise expire within this many seconds from now.

The purpose of this is to keep the session store from being updated when nothing else in the session is updated.

Defaults to 0 (in which case, the expiration will always be updated).

verify_address
When true, "$c->request->address" will be checked at prepare time. If it is not the same as the address that initiated the session, the session is deleted.

Defaults to false.

verify_user_agent
When true, "$c->request->user_agent" will be checked at prepare time. If it is not the same as the user agent that initiated the session, the session is deleted.

Defaults to false.

flash_to_stash
This option makes it easier to have actions behave the same whether they were forwarded to or redirected to. On prepare time it copies the contents of "flash" (if any) to the stash.

SPECIAL KEYS

The hash reference returned by "$c->session" contains several keys which are automatically set:
__expires
This key no longer exists. Use "session_expires" instead.
__updated
The last time a session was saved to the store.
__created
The time when the session was first created.
__address
The value of "$c->request->address" at the time the session was created. This value is only populated if "verify_address" is true in the configuration.
__user_agent
The value of "$c->request->user_agent" at the time the session was created. This value is only populated if "verify_user_agent" is true in the configuration.

CAVEATS

Round the Robin Proxies

"verify_address" could make your site inaccessible to users who are behind load balanced proxies. Some ISPs may give a different IP to each request by the same client due to this type of proxying. If addresses are verified these users' sessions cannot persist.

To let these users access your site you can either disable address verification as a whole, or provide a checkbox in the login dialog that tells the server that it's OK for the address of the client to change. When the server sees that this box is checked it should delete the "__address" special key from the session hash when the hash is first created.

Race Conditions

In this day and age where cleaning detergents and Dutch football (not the American kind) teams roam the plains in great numbers, requests may happen simultaneously. This means that there is some risk of session data being overwritten, like this:
1.
request a starts, request b starts, with the same session ID
2.
session data is loaded in request a
3.
session data is loaded in request b
4.
session data is changed in request a
5.
request a finishes, session data is updated and written to store
6.
request b finishes, session data is updated and written to store, overwriting changes by request a

For applications where any given user's session is only making one request at a time this plugin should be safe enough.

AUTHORS

Andy Grundman

Christian Hansen

Yuval Kogman, "[email protected]"

Sebastian Riedel

Tomas Doran (t0m) "[email protected]" (current maintainer)

Sergio Salvi

kmx "[email protected]"

Florian Ragwitz (rafl) "[email protected]"

Kent Fredric (kentnl)

And countless other contributers from #catalyst. Thanks guys!

Contributors

Devin Austin (dhoss) <[email protected]>

Robert Rothenberg <[email protected]> (on behalf of Foxtons Ltd.)

COPYRIGHT & LICENSE

    Copyright (c) 2005 the aforementioned authors. All rights
    reserved. This program is free software; you can redistribute
    it and/or modify it under the same terms as Perl itself.

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