RPX (https://rpxnow.com/) is a company that makes a single sign on service that lets the user sign in using one of various services, ie. google, facebook, msn, openid.
They have a voting system, that helps them decide which 3. party systems they develop plugins for.
Therefore please vote here so that they will consider implementing a moodle authentication plugin:
http://rpx.uservoice.com/forums/8895-general/suggestions/469463-make-a-moodle-plugin
Thanks
my 6 votes 
Giving it a bump ;)