GoLang Oauth2 using Google Application Default Credentials

main.go

package main

import (
	"context"
	"fmt"
	"log"
	"net/http"

	"golang.org/x/oauth2/google"
	"google.golang.org/api/oauth2/v2"
)

func appDefToken() string {
	ts, err := google.DefaultTokenSource(context.TODO(), oauth2.UserinfoEmailScope)
	if err != nil {
		log.Fatalf("token source: %v", err)
	}
	token, err := ts.Token()
	if err != nil {
		log.Fatalf("token: %v", err)
	}
	return token.AccessToken
}

func main() {
	oauthHttpClient := new(http.Client)
	oauth2Service, err := oauth2.New(oauthHttpClient)
	if err != nil {
		log.Fatalf("could not get service: %v", err)
	}

	token := appDefToken()
	info, err := oauth2Service.Tokeninfo().AccessToken(token).Do()
	if err != nil {
		log.Fatalf("Error: token error %v", err)
	}
	if info.Email != "" {
		fmt.Println(info.Email)
	} else {
		fmt.Println("No email for token: ", info)
	}
}