Single Sign On handler (SSO)

*Title: Single Sign On handler (SSO)

*Original author: Bard Farstad

*Documentation:
A single sign on(SSO) handler plugin system is introduced.
This means that you can run a piece of PHP code on every new instance of a
session. Here you can check if the user is already logged in with another
system and automatically log the user in to Exponential - without any typing
of passwords. The security and integration is handled by the specific plugins.

It adds a new setting in site.in under UserSettings:
SingleSignOnHandlerArray

This array defines the available single sign on handlers.

The handlers needs to be placed in an extension in the directory under
sso_handler. The sso handler needs to implement a class like shown below:
<?php
    include_once( 'kernel/classes/ezpersistentobject.php' );
    include_once( 'kernel/classes/datatypes/ezuser/ezuser.php' );
    include_once( 'lib/ezutils/classes/ezini.php' );

    class eZMysqlssohandler
    {
        function eZMysqlssohandler()
        {
        }

        /*!
          Return the eZUser object to log in or false if no user should be
          logged in.
        */
        function handleSSOLogin()
        {
            $currentUser =& eZUser::fetch( 14 );
            return $currentUser;
        }
    }
?>