I have read many solutions out there for sharing users and checked out the other posts on here, but can't find specifically what I'm after, as they all talk about users on the same database. Understand WP-config file and defining the custom user table, but I don't think this will work in my case as my setup is on two different databases. Some of the solutions are also quite old and sure they don't function with 4.1.1 anymore.
I have two different sites, each on their own database. Site A is where I want to share the user tables from. Site B is a multisite setup using subdomains. I need user data to be shared from site A to site B and any subdomains that site B may include. Site B will probably have in excess of 300 sites.
Users visiting site B, or any of its subdomains, need to be redirected to Site A for registration before being allowed access. What's the best way to achieve this?
Both sites will be on the same server so I hoping this will make things a little easier.
Any suggestions on how I can create the data to be shared? Ideally would like to do this without the use of plugins.