Working to integrate better with our portal and not worry about users passwords. I have used OAuth with PHP to create a channel between our portal and Google Apps.
First thing you need to do is setup OAuth Access on Google Apps.
1. Open Google Apps Control Panel
2. Click Advanced Tools
3. Click Manage OAuth Domain Key
4. Follow steps to provide you a OAuth Consumer Secret.
Integrating with PHP
Check out this site for example code to integrate into Google API’s with OAuth