Single Sign On - How To Implement It?

Two methods (off the top of my head):

1: Recode all the sites to use one login.
2: Write a PHP script that logs them in in the background.

Cost would vary by the scripts and programmer.

you could also try and use some kind of tracking like a cookie for login information that all your sites look for. once they login on one site the cookie is placed and if they go to another site the cookie will log them in automatically

Single Sign On is very complicated and likely very expensive so think carefully before you explore this option.

You will need to create your own user account system, which someone signing up to any of the services (or who is already signed up) gets an account on.

Each platform that you have a site built on (Joomla/Moodle etc) will need to have a new authorization mechanism created for it that contacts the central account store rather than using its own.

Those parts will get you as far as federated sign on. That's to say that have a central account will allow them to login to all of your sites but the login won't be carried across so they'll need to login at each site individually.

To get as far as a fully Google-esque SSO your login pages will need to be able to check if someone is already signed into the main system and redirect accordingly. (That's what's happening when you go to sign into a Google service when you're already logged in somewhere else and it says "loading" and redirects you).

SSO gets even more complicated still when you have to deal with permissions/access to the different sites. Eg instead of having a very open Google like setup where you just need an account and you can use everything you have a set of sites that require payment to access them, with payment only gaining you access to one site. To do that your central account/authorisation system needs to be even more complicated and hooked up to your payment processor so it can track which sites they can login to.

Don't wish to be a doom monger but just want to make sure you appreciate the scope of what you're looking to do here.

Cheers,

Andy

I've touched on the topic of SSO a couple of years back and the conclusion then is successful SSO implementation are for those big companies like Google and Yahoo. It seems virtually impossible for the small-medium dotcom to achieve SSO.

Until now, SSO seems to be technically tough as very few, without deep corporate pocket, are close to successful implementation.