Google API Oauth2 JWT Token

main.go

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"os"
	"time"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/chi/v5/middleware"
	"golang.org/x/oauth2"
	"golang.org/x/oauth2/google"
	"golang.org/x/oauth2/jwt"
)

func main() {
	r := chi.NewRouter()
	r.Use(middleware.Logger)

	r.Get("/google-token", func(w http.ResponseWriter, r *http.Request) {
		token := getTokenGoogle()

		w.Write([]byte(token))

	})

	http.ListenAndServe(":3000", r)
}

func getTokenGoogle() string {

	token, err := serviceAccount("key_account.json")
	if err != nil {
		fmt.Println(err)
		os.Exit(1)
	}

	return token.AccessToken
}

func serviceAccount(credentialFile string) (*oauth2.Token, error) {
	b, err := os.ReadFile(credentialFile)
	if err != nil {
		return nil, err
	}
	var c = struct {
		Email      string `json:"client_email"`
		PrivateKey string `json:"private_key"`
	}{}
	json.Unmarshal(b, &c)
	config := &jwt.Config{
		Email:      c.Email,
		PrivateKey: []byte(c.PrivateKey),
		Scopes: []string{
			"https://mail.google.com/",
      // can use other scopes google api...
		},
		TokenURL: google.JWTTokenURL,
		Expires:  time.Hour,
		Subject:  "sender@gmail.co",
	}

	token, err := config.TokenSource(context.Background()).Token()
	if err != nil {
		return nil, err
	}
	return token, nil
}