The organization I work for would benefit if we could take the existing WordPress installations that are located on several (~5) different servers and be able to use a universal database with the users table only. The individual servers would use a database for the remaining content.
The idea is this. Have a "main" server with all of the user's data (some 300+ users) which whom a network admin can give/edit permissions to these users on each of the other servers.
This way, when a user logs in to one WordPress installation on one server, the user could visit another WordPress server and still be logged in with various permissions on the various servers.
This would be a 1:1 relationship for WordPress Network to Server. How would cookies or sessions need to be utilized in order to allow this?
Would an outside API login system need to be used in order to accomplish this? Or could this be done within the WordPress core files?