Google AuthSubRequest: Password required twice?

Question

I am using AuthSub to access Google Analytics API Data. I think I must be doing something wrong because it requires the end user to provide the google password twice. Here are the steps:

1. My application makes AuthSubRequest call.
2. Google returns with a html page which has a google account login form. This page has a post to google.
3. I display the page returned in step (2) within my site. So it is a google login page but the url is a page on my domain. In my point of view, this looks as if my site is "faking" a google login.
4. The user enters email and password. On successful login they are redirected to a login page on the google domain. The email address is already specified, but the password is required again.
5. Once the user successfully authenticates, the browser is redirected to the url I specified in the "Next" parameter.

Is this correct sequence? I would have thought only one authentication is required directly from the google site. Instead I am rendering a google login from my own site only to have the user redirected to google to authenticate again.

Thanks.