It is very convenient to have people log on a wiki with Google credential. Thanks for Bertrand Gorge and Emanuele Nanetti for the great work.
http://www.mediawiki.org/wiki/Extension:GoogleAppsAuthentification
An issue is that sometimes, even with Google return the right credential, mediawiki (19.2) does not get people log in correctly.
So far, I found the root cause was with SpecialUserlogin.php and patched it. Detail is here.