Using the settings.php shared behavior your sites should be inside the same db/server using a differents prefix and the user/sessions table using the same prefix. A example:
Web site A settings.php
$db_prefix = array(
      'default'   => 'site_a_',
      'users'     => 'shared_',
      'sessions'  => 'shared_',
      'role'      => 'shared_',
      'authmap'   => 'shared_',
    );

Web site B settings.php
$db_prefix = array(
      'default'   => 'site_b_',
      'users'     => 'shared_',
      'sessions'  => 'shared_',
      'role'      => 'shared_',
      'authmap'   => 'shared_',
    );

Using diferents servers and dbs, maybe you should think about another authentication type, something based on directories. Write your own authentication module is always a option.

Att,

Pablo Lacerda de Miranda
Analista de Sistemas
Pontifícia Universidade Católica de São Paulo
pablolmiranda@gmail.com
+55 11 8701-1086


On Fri, Jul 30, 2010 at 5:08 PM, Michel Morelli <michel@ziobuddalabs.it> wrote:
Pablo L. de Miranda ha scritto:
> Take a look on the settings.php file, there has a information how you
> can share tables between one or more sites. So, you just can share the
> user and sessions table between your sites..
Two different db/server ???
Ah, thanks.

M.



--
Michel 'ZioBudda' Morelli                       michel@ziobuddalabs.it
Sviluppo applicazioni CMS DRUPAL e web dinamiche (LAMP+Ajax)
Telefono: 0200619074
Telefono Cell: +39-3939890025 --  Fax: +39-0291390660

http://www.ziobudda.net                         ICQ: 58351764
http://www.ziobuddalabs.it                      Skype: zio_budda
http://www.ziodrupal.net                        MSN: michel@ziobuddalabs.it
                                               JABBER: michel@ziobuddalabs.it

--
[ Drupal support list | http://lists.drupal.org/ ]