Question

I have this idea to unify 10 systems, they will all share the same user which will only login to the principal site, after that he will be able to log to any separated system without having to login again. What’s the best way to accomplish this?

I’m using php and mysql on all my systems.

they are all running on the same domain, same server. They use different databases for each.

Answer 1

Well, without full details its hard to say. I’ve done this and its actually not so difficult. The trick is to have all of your users in a common database, or to create a common piece of code that all websites use for user validation that will individually scan all user databases.

If your apps are sub-domains of a single domain, have a look at these docs

ini_set("session.cookie_domain", ".domain.com");