Multisite + Shared Login Information with separate domain names.

Hello,

I am looking to create 2 separate Drupal sites using Drupal's built-in multisite capability.

The two sites should have shared username and password so that the same username and password could be used on either site.

I have read that Drupal's built-in multisite capability can handle this feature and share the same username and password across the two separate sites. However, I have also read that this only works if using sub-domains. (site1.domain.com and site2.domain.com).

What I would like to do is have two, completely different domains for each site. (site1.com and site2.com).

So my question is, how can I setup two Drupal sites with shared login information, where each site has its own domain name?