Make sure you have set your cookie-policy to a value other than none
in your sign-in button code. For example:
function handleAuthClick(event) {
gapi.auth.authorize(
{
client_id: clientId,
scope: scopes,
immediate: false,
cookie_policy: 'single_host_origin'
},
handleAuthResult);
return false;
}
Note that sign out will not work if you are running from localhost.