I am working on a project of integrating Drupal with an existing site that has a members login, the drupal site would only be accessible by members that have logged into the main site. So for instance:

User accesses www.site.com
Logs in to members only site
Now can access the drupal site drupal.site.com

My question is what is the best way to do this, we don't want users to log in twice, or to have to recreate the users in drupal each time a new user registers on the main site.

Thanks

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Chris McCreery