We've got our LDAP connected portal developed in an IIS7 PHP environment. We've been tasked with integrating Google Apps, so that once a user is signed in to our portal, they can simply click and icon for Gmail or Google Calendar, and be signed in to their Google Apps for Education account. From what I understand, it's necessary to send the information to an Identity Provider before sending the credentials to Google.
Is there an open source solution, or collection of solutions that can provide this, or must we choose a paid service?