code sample for Google API oauth using GoLang

ga.go

// Hello, hope you find this code useful
package main

import (
	// this is a deprecated oauth lib from godoc.org
	// i was going to use the new one (https://godoc.org/golang.org/x/oauth2/google)
	// but due to a bug i've found and filed at github
	// i decided to revert to the old one instead until the new one is stable
	"code.google.com/p/goauth2/oauth/jwt"
	"encoding/json"
	"io/ioutil"
	"net/http"
	"os"
	
	// optional, this is just a logger
	log "github.com/Sirupsen/logrus"
)

// REQUIREMENTS: credentials for OAuth and HTTP Request
var (
	// KEYS retrieved from Google Developer Console
	// also add Service Email in Analytics as another user
	gaServiceEmail = "[email protected]"
	// Private Key can be found inside JSON file downloaded from Dev Console
	gaPrivateKey = []byte("<------ BEGIN HERE ------>...")
	gaApiKey     = "lkjf98hs--- SOME GIBBERISH KEY ---98hsdjif"

	// Service: URLs can be found at
	// https://developers.google.com/analytics/devguides/config/
	// under Reference and Resources
	// or refer to Google APIs Explorer inside Google Developer Console
	gaScope           string = "https://www.googleapis.com/auth/analytics"
	gaAccountId       string = "xxxxxx"
	gaWebPropertyId   string = "UA-xxxxxxx-x"
	gaProfileId       string = "xxxxxxx"
	gaGoalsUrlRequest string = "https://www.googleapis.com/analytics/v3/management/accounts/" + gaAccountId + "/webproperties/" + gaWebPropertyId + "/profiles/" + gaProfileId + "/goals"
)

type Item struct {
	Name string `json:"name"`
}

type GAReportData struct {
	Kind  string `json:"kind"`
	Items []struct {
		Item
	} `json:"items"`
}

// README
// https://developers.google.com/accounts/docs/OAuth2ServiceAccount
// Explains OAuth2 Service Account flow and how code works
func getGAReportData() (err error) {
	client := &http.Client{}

	// Create JWT and jwt.NewToken does all the magic!
	gaToken := jwt.NewToken(gaServiceEmail, gaScope, gaPrivateKey)
	// Request access token to Google with client and JWT credentials
	gaAccessToken, err := gaToken.Assert(client)
	if err != nil {
		log.Error("GA Report - Unable to request Access Token: ", err)
		return
	}

	// Establish connection to the Service with access token
	req, err := http.NewRequest("GET", gaGoalsUrlRequest+"?key="+gaApiKey, nil)
	req.Header.Set("Authorization", "Bearer "+gaAccessToken.AccessToken)
	resp, err := client.Do(req)
	if err != nil {
		log.Error("GA Report - Unable to establish connection: ", err)
		return
	}
	defer resp.Body.Close()

	// Read response data
	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		log.Error("GA Report - Unable to read data: ", err)
		return
	}

	// Decode data and get necessary data only
	data := &GAReportData{}
	err = json.Unmarshal(body, data)
	if err != nil {
		log.Error("GA Report - Unable to decode data: ", err)
		return
	}

	// Encode data
	// TODO
	// use MarshalIndent to prettify for viewing/debugging purpose
	// but use Marshal after
	prettybody, _ := json.MarshalIndent(data, "", " ")
  	log.Debug("GA Report JSON: \n", string(prettybody))

  return
}

// If you have any questions, please feel free to contact me, I'd be happy to assist you. :-)