Using OAuth 2.0 for Server to Server Applications and the Google Analytics API with node.js.

poc-ga.js

/**
 * Module dependencies
 */

var GA = require('googleanalytics'),
	jwt = require('jwt-sign'),
	request = require('superagent'),
	fs = require('fs'),
	privateKey = fs.readFileSync(process.env['GA_PATH_PRIVATE_KEY'] || __dirname + '/key/private.pem','utf8');

// Configuration
var PROFIL_ID = process.env['GA_PROFIL_ID'] || '49870159';
var EMAIL_ADDRESS = process.env['GA_EMAIL_ADDRESS'] || '[email protected]';

// JWT payload
var payload = {
    'iss': EMAIL_ADDRESS,
    'scope': 'https://www.googleapis.com/auth/analytics.readonly',
    'aud':'https://accounts.google.com/o/oauth2/token',
    'exp': ~~(new Date().getTime() / 1000) + (30 * 60),
    'iat': ~~(new Date().getTime() / 1000 - 60)
};

// Sign the payload with the private key
var signed = jwt.sign(payload,privateKey);

// Request the access token
request.post('https://accounts.google.com/o/oauth2/token')
	.set('Content-Type','application/x-www-form-urlencoded')
	.set('Accept','application/json')
	.send({
		'grant_type' : 'urn:ietf:params:oauth:grant-type:jwt-bearer',
		'assertion' : signed
	})
	.end(function(err, res){
		if(err) return console.error(err);

		var accessToken = res.body.access_token;
		if(!accessToken) throw new Error('access token is empty!');

		// Google analytics client
		var ga = new GA.GA({
			'token' : accessToken
		});

	    var options = {
	        'ids': 'ga:' + PROFIL_ID,
	        'start-date': '2013-02-01',
	        'end-date': '2013-02-25',
	        'dimensions': 'ga:hostname', //ga:customVarValue(n)
	        'metrics': 'ga:visitors,ga:newVisits,ga:visits,ga:pageviews'
	        //'sort': ''
	    };

	    // Request the report
	    ga.get(options, function(err, entries) {
	    	if(err) return console.error(err);
	    	console.log(JSON.stringify(entries,null,'\t'));
	    });
});