How to achieve automatic authentication using GCE Go client oauth2 authentication - go

Question

This code is on the basis of golang.org/x/oauth2 example test. I am trying to get instance information from Google Compute Engine using Go client. Do I have to use oauth2 authentication? There is a generated link after Visit the URL for the auth dialog:
https://accounts.google.com/o/oauth2/auth?access_type=offline&client_id=xxx&redirect_uri=https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fcompute&response_type=code&scope=https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fcompute&state=state
and it redirect to https://www.googleapis.com/auth/compute which shows a 'compute'.
How do I achieve automatic authentication?
package main
import (
"context"
"fmt"
"log"
"golang.org/x/oauth2"
"google.golang.org/api/compute/v1"
)
type GCE struct {
*compute.Service
}
var ctx = context.Background()
func initGCE() *GCE {
conf := &oauth2.Config{
ClientID: "xxx",
ClientSecret: "xxx",
Scopes: []string{compute.ComputeScope},
Endpoint: oauth2.Endpoint{
AuthURL: "https://accounts.google.com/o/oauth2/auth",
TokenURL: "https://accounts.google.com/o/oauth2/auth",
},
RedirectURL: "https://www.googleapis.com/auth/compute",
}
url := conf.AuthCodeURL("state", oauth2.AccessTypeOffline)
fmt.Printf("Visit the URL for the auth dialog: %v", url)
var code string
if _, err := fmt.Scan(&code); err != nil {
log.Fatal(err)
}
tok, err := conf.Exchange(ctx, code)
if err != nil {
log.Fatal(err)
}
service, err := compute.New(conf.Client(ctx, tok))
if err != nil {
log.Fatal(err)
}
return &GCE{service}
}
func (g *GCE) Instance() {
project := "arctic-cyclist-189707"
zone := "us-east1-b"
instance := "centos7"
resp, err := g.Instances.Get(project, zone, instance).Context(ctx).Do()
if err != nil {
fmt.Println(err)
return
} else {
fmt.Printf("%#v\n", resp)
}
}

Answer 1

Solved by using code example
https://cloud.google.com/compute/docs/reference/latest/instances/get#examples
just set "GOOGLE_APPLICATION_CREDENTIALS" environment varibles as google.DefaultClient() requires.
package main
import (
"context"
"fmt"
"log"
"golang.org/x/oauth2/google"
"google.golang.org/api/compute/v1"
)
type GCE struct {
*compute.Service
}
var ctx = context.Background()
func initGCE() *GCE {
c, err := google.DefaultClient(ctx, compute.CloudPlatformScope)
if err != nil {
log.Fatal(err)
}
computeService, err := compute.New(c)
if err != nil {
log.Fatal(err)
}
return &GCE{computeService}
}
func (g *GCE) Instance(project, zone, instance string) {
resp, err := g.Instances.Get(project, zone, instance).Context(ctx).Do()
if err != nil {
log.Fatal(err)
}
fmt.Printf("%#v\n", resp)
}
Thanks for your reply.