There is controlled access that allow only users who have a Confluence account to see a Confluence Cloud Space and the other option is full anonymous access who provides access to anyone in the Internet.

I know whitelist is in progress to restrict access to a particular IP, but it would be great if there was a middle ground that allowed anyone with a *@companydomain.com email address (possibly authenticated by O365 or any other third party Identity provider) to have read only access to a Confluence Space without the need of a full license.  

Thank you