by David Perry.
I couldn't find anything about a free SAML IdP plugin for moodle (which would achieve the same thing - we use Shibboleth, so basically SAML, to SSO into Google Apps from a college network account).
This company came up in a search, and even though the article is for old moodle (2.0) they might be able to adapt one of their products to use moodle as the login source: