The callback url should be SSL enabled.
To do this you might have to re register your application with Connection server. This might help : http://www-10.lotus.com/ldd/lcwiki.nsf/xpDocViewer.xsp?lookupName=IBM+Connections+4.0+documentation#action=openDocument&res_title=Registering_an_OAuth_client_with_a_provider_ic40&content=pdcontent