A pam module , authenticate by ocs.
It is the first step for my online account plan.
In this plan, we use gdm to login by the online account.
After that, the online account info will keep in 'gnome-session'.
Maybe I'll write a new 'online-session'.
This session's role is like 'cookie' in web.

As ocs have friends, activitys, apps, 
the following usage of our online account system is quite easy,
we have the message, activitys..

Most important: we need to have S3 like dist service.
Which is for us to have a basic home dir.

Now just support the plain user/password.
In the long term, will support oauth and the etc, but need to modify GDM lot.
Need to have deep understanding about gnome-online-account.