Single Sign-In For Multiple PHP Websites


Staff member
I am having four different php websites. First website is implemented in codeigniter, second one is implemented in core php, third and fourth websites are implemented in wordpress. All 4 websites are <strong>having different logins</strong>(user authentication).

Now i want to change user authentication for all my sites. <strong>I want my users to use one single email-id and password for my 4 websites</strong>. If user, login into any website, then he should be <strong>able to automatically login into other 3 websites</strong> without asking login again(similar to, with one google account, we can login into googleplus,youtube,maps,drive).

I can keep all my four php websites under one domain(using sub-domains). But i don't no how to achieve single sign-in for all 4 different websites.

<strong>My big concern is, i am using 4 different databases for 4 websites. Every database is having its own "users table". Now how can i integrate one login for all 4 websites</strong>

I dont want to use "login through gmail or login through facebook". i want to have my own login system for all my websites

Can anyone suggest me, from where i should start?