google.go

//Code from https://developers.google.com/apps-script/guides/rest/quickstart/go
//Modified to support refreshing tokens
package main

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"os"

	"golang.org/x/net/context"
	"golang.org/x/oauth2"
	"golang.org/x/oauth2/google"
)

const tokenFile = "./token.credential"

// GetClient returns the generated Client.
func GetClient(scopes ...string) *http.Client {
	b, err := ioutil.ReadFile("client_secret.json")
	if err != nil {
		log.Fatalf("Unable to read client secret file: %v", err)
	}

	config, err := google.ConfigFromJSON(b, scopes...)
	if err != nil {
		log.Fatalf("Unable to parse client secret file to config: %v", err)
	}

	tok, err := tokenFromFile(tokenFile)
	if err != nil {
		tok = getTokenFromWeb(config)
		saveToken(tokenFile, tok)
	}
	ctx := context.Background()
	//Very hacky, but somehow works
	ts := oauth2.ReuseTokenSource(nil, config.TokenSource(ctx, tok))
	t, _ := ts.Token()
	return config.Client(ctx, t)
}

// getTokenFromWeb uses Config to request a Token.
// It returns the retrieved Token.
func getTokenFromWeb(config *oauth2.Config) *oauth2.Token {
	authURL := config.AuthCodeURL("state-token", oauth2.AccessTypeOffline)
	fmt.Println(authURL)

	var code string
	if _, err := fmt.Scan(&code); err != nil {
		log.Fatalf("Unable to read authorization code %v", err)
	}

	tok, err := config.Exchange(oauth2.NoContext, code)
	if err != nil {
		log.Fatalf("Unable to retrieve token from web %v", err)
	}
	return tok
}

// tokenFromFile retrieves a Token from a given file path.
// It returns the retrieved Token and any read error encountered.
func tokenFromFile(file string) (*oauth2.Token, error) {
	f, err := os.Open(file)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	t := &oauth2.Token{}
	err = json.NewDecoder(f).Decode(t)
	return &oauth2.Token{RefreshToken: t.RefreshToken}, err
}

// saveToken uses a file path to create a file and store the
// token in it.
func saveToken(file string, token *oauth2.Token) {
	log.Printf("Saving credential file to: %s\n", file)
	f, err := os.Create(file)
	if err != nil {
		log.Fatalf("Unable to cache oauth token: %v", err)
	}
	defer f.Close()
	json.NewEncoder(f).Encode(token)
}