Generate Open ID Token Connect with Google Service Account Key

exmaple.go

package main

import (
        "context"
        "errors"
        "flag"
        "fmt"
        "io/ioutil"
        "log"

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

var (
        keyFile = flag.String("key-file", "", "private pem key file for the service account")
        url     = flag.String("url", "", "target url")
)

func client(ctx context.Context, keyFile, targetAudience string) (*http.Client, error) {
        // Read the key file bytes for the private key.                                                                                     
        keyBytes, err := ioutil.ReadFile(keyFile)
        if err != nil {
                return nil, err
        }
        cfg, err := google.JWTConfigFromJSON(keyBytes)
        if err != nil {
                return nil, err
        }
        cfg.PrivateClaims = map[string]interface{}{"target_audience": targetAudience}
        cfg.UseIDToken = true
        return cfg.Client(ctx), nil
}

func main() {
        flag.Parse()
        if *keyFile == "" || *url == "" {
                log.Fatal("Please specifiy --key-file <service_account_key> and --url <URL>")
        }
        cl, err := client(context.Background(), *keyFile, *url)
        if err != nil {
                log.Fatal("%v", err)
        }
        resp, err := cl.Get(*url)
        if err != nil {
                log.Fatal("%v", err)
        }
        defer resp.Body.Close()
        body, err := ioutil.ReadAll(resp.Body)
        if err != nil {
                log.Fatal("%v", err)
        }
        fmt.Printf("%s", string(body))
}