NAME
    Catalyst::Plugin::Session - Generic Session plugin - 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 simply a hexidecimal string of raw bytes from the system
        entropy source, e.g. /dev/urandom.

    session_hash_seed
        This method returns raw bytes from the system random source. It is
        no longer used but exists for legacy code that might override
        "generate_session_id" but still uses this method.

    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, "nothingmuch@woobling.org"

    Sebastian Riedel

    Tomas Doran (t0m) "bobtfish@bobtfish.net" (current maintainer)

    Sergio Salvi

    kmx "kmx@volny.cz"

    Florian Ragwitz (rafl) "rafl@debian.org"

    Kent Fredric (kentnl)

    And countless other contributers from #catalyst. Thanks guys!

Contributors
    Devin Austin (dhoss) <dhoss@cpan.org>

    Robert Rothenberg <rrwo@cpan.org>

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.