Limit OpenID to drupal.org and invuted sites

I would like to open up demo sites to people invited from specific sites including drupal.org. Can I do it with OpenID? What are the alternatives?

The site demonstrates themes and modules in Drupal. I figure anyone from drupal.org should be able to login using their drupal login through Open ID or similar, whatever groups.drupal.org uses, so they can experiment with the settings for the themes and modules. I do not want to let other people access the same settings because I would have to spend years explaining the basics of Drupal to everyone who registers, logs in, then changes all the settings without reading anything about Drupal.

I also want to allow access to some users from other sites when they are considering upgrading to Drupal. I am thinking of creating a drupal_demo role and manually adding the role where needed. I would like to have the role added automatically to visitors from drupal.org.