Convert Google Service Account Private Key (stdin) to JWT Token

sajwt.go

package main

//
// this converts a google service account key to a jwt
//
import (
	"encoding/json"
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"os"

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

func main() {
	b, err := ioutil.ReadAll(os.Stdin)
	if err != nil {
		log.Fatal(err)
	}

	var audience = flag.String("audience", "", "audience")

	// generate token
	source, err := google.JWTAccessTokenSourceFromJSON(b, *audience)
	if err != nil {
		log.Fatal(err)
	}

	token, err := source.Token()
	if err != nil {
		log.Fatal(err)
	}

	json, err := json.Marshal(token)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Printf("%s", json)
}

export GOOGLE_APPLICATION_CREDENTIALS=service-account.json
cat $GOOGLE_APPLICATION_CREDENTIALS | go run sajwt.go

{"access_token":"<redacted>","expiry":"2019-09-18T18:13:21.343128-06:00","token_type":"Bearer"}