Multiple WordPress websites with single user registration?

Question

I have been searching for couple of days how to join users but have separated websites on WordPress.

I know there is WordPress Multi User option, but it's not quite what I wanted. As I understood Wordpress MU works on single domain installation.

But I have 3 websites they all have their own content and different domain names and separated registrations. What I am searching is to have them joined as a network. So single user registration for all sites, basically when user register on any of them he can login on other sites too, and user interaction to be joined on all sites. But to keep content separated, so one website is about cooking and I want it to remain about cooking, other is about cars and I want it like that. Third is about games and I want it to stay about games. But instead that one user register 3 times on all 3 websites user can register only 1 time and get access on all 3 websites.

Answer 1

Yes, what you need is WordPress Multisite (previously known as WordPress MU, or WPMU).
Plus the Domain Mapping plugin, which will take care of making the sub-site work as a Top Level Domain.

Multisite is installed to work with sub-domains or with folders: http://subsite.example.com or http://example.com/subsite. What the plugin does is to map something like http://client.net or http://microsite.client.net to a selected sub-site. It's practically transparent, the visitor doesn't know he's looking at a sub-site.

^{Check the wiki with Multisite resources at WordPress Answers.
Hints: 1) It's extremely important to watch exactly what plugins and themes you're installing. Reputable sources, stable code. 2) If backup and security measures are important in any site, in Multisite multiply that by the number of sites running and a bit more.}

Answer 2

I think you're looking for this solution:

Multiple Databases, Same Users

You can use the same userbase with all your blogs on the same domain, by defining the CUSTOM_USER_TABLE and optionally the CUSTOM_USER_META_TABLE constants to point to the same wp_your_blog_usermeta and wp_your_blog_users tables.

It does say on the same domain, but could be easily modified to work in your situation. The idea is to use a common database.