
You are correct: the sessions cannot be shared across domains. The only way to solve it is to have a Resource on the target domain where manager users can login to that context and get permission to view_unpublished. But the client browser has to get a session cookie set from the target domain.
Can I use the "Login" snippet to create a manager session?You don't want a mgr session, you need to Login to the Context handling the domain you need the session cookie from. And you will need a Policy associated with that User (via User Group membership) that is attached to the Context which includes the view_unpublished permission (I would create a Policy with load, list, view, save, remove, add_children and view_unpublished permissions which you can give to your manager users for this Context. Then you just use Login to login to that Context; once logged in, you can see the unpublished Resources in that browser session.
Would I be able to use curl to do a backround login in a plugin so my manager users dont have to login twice?Not that I know of; the session cookie has to be returned from the target domain directly to the client browser AFAIK.
Could possibly work if that meets your needs.
The manager is isolated on one domain.
Front end on another.....
What about if I setup a folder on the managers domain, that has the front end index.php and config.inc.php, and just use that for "view resource" and preview etc. They would not be seeing the preview on the final domain....but I don't think that an issue.
The user would preview on mymanager.mysite.com/frontend/