Access Gmail account with a service Account in Go (Golang)

golang-gmail-service-account.go

package main

import (
	"fmt"
	"google.golang.org/api/gmail/v1"
	"io/ioutil"
	"log"

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

	admin "google.golang.org/api/admin/directory/v1"
	"google.golang.org/api/option"
)

// Path to the Service Account's Private Key file
var ServiceAccountFilePath = "your-private-key-for-service-account.json"


// Build and returns a Gmail service object authorized with Service Account

func CreateGmailService(userEmail string) (*gmail.Service, error) {
	ctx := context.Background()

	jsonCredentials, err := ioutil.ReadFile(ServiceAccountFilePath)
	if err != nil {
		return nil, err
	}

	config, err := google.JWTConfigFromJSON(jsonCredentials, gmail.MailGoogleComScope)
	if err != nil {
		return nil, fmt.Errorf("JWTConfigFromJSON: %v", err)
	}

	config.Subject = userEmail
	ts := config.TokenSource(ctx)

	srv, err := gmail.NewService(ctx, option.WithTokenSource(ts))
	if err != nil {
		return nil, fmt.Errorf("NewService: %v", err)
	}
	return srv, nil
}

func main() {

	emailId := "your.email@yourdomain.com"
	service, err := CreateGmailService(emailId)

	if err != nil {
		log.Fatalf("Unable to retrieve labels: %v", err)
	}

	r, err := service.Users.Labels.List(emailId).Do()
	if err != nil {
		log.Fatalf("Unable to retrieve labels: %v", err)
	}
	if len(r.Labels) == 0 {
		fmt.Println("No labels found.")
		return
	}
	fmt.Println("Labels:")
	for _, l := range r.Labels {
		fmt.Printf("- %s\n", l.Name)
	}

}