Google IDP Authorization and Google Apps

Google IDP Authorization and Google Apps

How does the Google IDP Authorization work with Google Apps? We are using our own domain for Google Apps.

Clicking on the "Sign In Using Google" link takes you to a page where you can only sign in with an "@gmail" account. I don't see any option to sign in with a Google account with a custom domain.

Apologize if this is a double post - I got an error on the first one.
dvalerian_ntc