[support] unified login for multiple domains

[Hugh Esco]

I've been reading through forum threads on the drupal site (mostly a
year or two old), trying to piece together how it is I would provide for
a single unified login that would permit folks to interlink between
multiple instances of drupal at a handful of third level domains
providing different services to the volunteers and members of an
organization as well as the folks they attract to their public site.  

I'd be happy to draft a Handbook page on the subject if I could get some
clarification and direction from those who have plowed this row before. 

One of these sites hosts civicrm and serves as a back office application
server to support distributed volunteers working together.  Another will
be a members site, plus a blog, plus perhaps another public site.  

What I've figured out so far, is summed up with:

in each sites/tld.ourdomain.org/settings.php
ini_set('session.cookie_domain', 'ourdomain.org');

 *   $db_prefix = array(
 *     'default'   => 'tld_',
 *     'users'     => 'shared_',
 *     'sessions'  => 'shared_',
 *     'role'      => 'shared_',
 *     'authmap'   => 'shared_',
 *     'sequences' => 'shared_',
 *   );

And here is where I'm guessing to bridge it all together, creating VIEWs
for each of those shared_ tables which looks instead at a single user
table; at which domain or database, I;m not sure.  

We want to collect that data in our crm instance, but I'd prefer not to
expose that to the public.  

I want someone who has logged in to www. or blog. to not face an
additional log in when they look at members. or crm, but to be turned
away if their user shouldn't be on those sites.  

I thought I'd outline this here and ask for feedback on this general
approach before getting lost in a trial by error forced march.  Has
anyone who has done this before know how to best proceed here?  Am I on
the right track with the sql views?  I'd certainly apreciate some
direction.  

Thanks, 
-- Hugh Esco