The default value of this parameter is 'false'. If it is set to 'true', the user is forced to provide their social network credentials during login - even if the user is already connected to the social network. This parameter is currently supported by Facebook, Twitter, and Renren. Note that the behavior of the various social networks may be slightly different: Facebook expects the current user to enter their password, and will not accept a different user name. Other networks prompt the user to re-authorize the application or allow a different user to log in.