// first call gapi.auth.authorize with immediate:true:
 _checkAuth = function _checkAuth(){
        gapi.auth.authorize({
            client_id : 'XXXXXXXXXXXXXXXXXXXXXXXXXX.apps.googleusercontent.com',
            scope : 'https://www.googleapis.com/auth/plus.login',
            request_visible_actions : 'http://schemas.google.com/CreateActivity',
            immediate : true
        }, function(authResult){
            if(!authResult || authResult.error){
               _signIn();
            }else{
                _performAction();
            }
        });
    },

// if not logged in, call gapi.auth.authorize with immediate:false:
_signIn = function _signIn(){
        gapi.auth.authorize({
            client_id : 'XXXXXXXXXXXXXXXXXXXXXXXXXX.apps.googleusercontent.com',
            scope : 'https://www.googleapis.com/auth/plus.login',
            request_visible_actions : 'http://schemas.google.com/CreateActivity',
            immediate : false
        }, function(token){
            gapi.auth.setToken(token);
           _performAction();
        });
    },

// create activity
_performAction = function _performAction(){
        gapi.client.load('plus','v1', function(){
            gapi.client.setApiKey('XXXXXXXXXXXXXXXXXXXXXXX');
            var payload = {
                "type" : 'http://schemas.google.com/CreateActivity'
            };
            payload.target = {
                "id" : "myappid",
                "image" : "http://www.example.com/xxxxxxxxxxx.jpg",
                "type" : 'http://schema.org/CreativeWork',
                "description" : "description of activity",
                "name" : "name of activity"
            };
            var args = {
                'path' : '/plus/v1/people/me/moments/vault',
                'method' : 'POST',
                'body' : JSON.stringify(payload),
                'callback' : function(response) {
                    console.log(response);
                }
            };
            gapi.client.request(args);

        });
    },