Google Cross Domain Authentication

Question

I have various sites (on their own domain) with their own authentication systems. What I'm trying to do is combine all the authentication into Google's authentication so the users will only have to log in with their Google credentials. What I'm thinking of is that they would log in with their Google credentials and be redirected to a dashboard which has image links to the other sites. The user should be able to go to any of the sites and be automatically logged in since they were already authenticated. I saw that there's an authentication for Google Apps but is this the same thing for my websites?

What I'm not sure about is how does this happen cross domain? How do the other domains know that the user is already authenticated? Also, if the user logs out, they should not be able to access any of the sites anymore. Anyone have any experience implementing something like this? Any resources are much appreciated. I will be implementing this in Coldfusion so Coldfusion resources are a bonus.

Answer 1

Your talking about using Google to login/signup i.e. Using OAuth 2.0.

You will need to register each of your app domains with Google. The user will need to confirm each application to allow access (in your case for signup/login).

Resource on Google Login with ColdFusion by Raymond Camden

The point is you need to establish a certain protocol to build a trust.

Other options are:

Google oauth javascript cross domain