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// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package google provides support for making OAuth2 authorized and
// authenticated HTTP requests to Google APIs.
// It supports the Web server flow, client-side credentials, service accounts,
// Google Compute Engine service accounts, and Google App Engine service
// accounts.
// For more information, please read
// and
package google
import (
// Endpoint is Google's OAuth 2.0 endpoint.
var Endpoint = oauth2.Endpoint{
AuthURL: "",
TokenURL: "",
// JWTTokenURL is Google's OAuth 2.0 token URL to use with the JWT flow.
const JWTTokenURL = ""
// ConfigFromJSON uses a Google Developers Console client_credentials.json
// file to construct a config.
// client_credentials.json can be downloaded from
//, under "Credentials". Download the Web
// application credentials in the JSON format and provide the contents of the
// file as jsonKey.
func ConfigFromJSON(jsonKey []byte, scope ...string) (*oauth2.Config, error) {
type cred struct {
ClientID string `json:"client_id"`
ClientSecret string `json:"client_secret"`
RedirectURIs []string `json:"redirect_uris"`
AuthURI string `json:"auth_uri"`
TokenURI string `json:"token_uri"`
var j struct {
Web *cred `json:"web"`
Installed *cred `json:"installed"`
if err := json.Unmarshal(jsonKey, &j); err != nil {
return nil, err
var c *cred
switch {
case j.Web != nil:
c = j.Web
case j.Installed != nil:
c = j.Installed
return nil, fmt.Errorf("oauth2/google: no credentials found")
if len(c.RedirectURIs) < 1 {
return nil, errors.New("oauth2/google: missing redirect URL in the client_credentials.json")
return &oauth2.Config{
ClientID: c.ClientID,
ClientSecret: c.ClientSecret,
RedirectURL: c.RedirectURIs[0],
Scopes: scope,
Endpoint: oauth2.Endpoint{
AuthURL: c.AuthURI,
TokenURL: c.TokenURI,
}, nil
// JWTConfigFromJSON uses a Google Developers service account JSON key file to read
// the credentials that authorize and authenticate the requests.
// Create a service account on "Credentials" for your project at
// to download a JSON key file.
func JWTConfigFromJSON(jsonKey []byte, scope ...string) (*jwt.Config, error) {
var f credentialsFile
if err := json.Unmarshal(jsonKey, &f); err != nil {
return nil, err
if f.Type != serviceAccountKey {
return nil, fmt.Errorf("google: read JWT from JSON credentials: 'type' field is %q (expected %q)", f.Type, serviceAccountKey)
scope = append([]string(nil), scope...) // copy
return f.jwtConfig(scope), nil
// JSON key file types.
const (
serviceAccountKey = "service_account"
userCredentialsKey = "authorized_user"
// credentialsFile is the unmarshalled representation of a credentials file.
type credentialsFile struct {
Type string `json:"type"` // serviceAccountKey or userCredentialsKey
// Service Account fields
ClientEmail string `json:"client_email"`
PrivateKeyID string `json:"private_key_id"`
PrivateKey string `json:"private_key"`
TokenURL string `json:"token_uri"`
ProjectID string `json:"project_id"`
// User Credential fields
// (These typically come from gcloud auth.)
ClientSecret string `json:"client_secret"`
ClientID string `json:"client_id"`
RefreshToken string `json:"refresh_token"`
func (f *credentialsFile) jwtConfig(scopes []string) *jwt.Config {
cfg := &jwt.Config{
Email: f.ClientEmail,
PrivateKey: []byte(f.PrivateKey),
PrivateKeyID: f.PrivateKeyID,
Scopes: scopes,
TokenURL: f.TokenURL,
if cfg.TokenURL == "" {
cfg.TokenURL = JWTTokenURL
return cfg
func (f *credentialsFile) tokenSource(ctx context.Context, scopes []string) (oauth2.TokenSource, error) {
switch f.Type {
case serviceAccountKey:
cfg := f.jwtConfig(scopes)
return cfg.TokenSource(ctx), nil
case userCredentialsKey:
cfg := &oauth2.Config{
ClientID: f.ClientID,
ClientSecret: f.ClientSecret,
Scopes: scopes,
Endpoint: Endpoint,
tok := &oauth2.Token{RefreshToken: f.RefreshToken}
return cfg.TokenSource(ctx, tok), nil
case "":
return nil, errors.New("missing 'type' field in credentials")
return nil, fmt.Errorf("unknown credential type: %q", f.Type)
// ComputeTokenSource returns a token source that fetches access tokens
// from Google Compute Engine (GCE)'s metadata server. It's only valid to use
// this token source if your program is running on a GCE instance.
// If no account is specified, "default" is used.
// Further information about retrieving access tokens from the GCE metadata
// server can be found at
func ComputeTokenSource(account string) oauth2.TokenSource {
return oauth2.ReuseTokenSource(nil, computeSource{account: account})
type computeSource struct {
account string
func (cs computeSource) Token() (*oauth2.Token, error) {
if !metadata.OnGCE() {
return nil, errors.New("oauth2/google: can't get a token from the metadata service; not running on GCE")
acct := cs.account
if acct == "" {
acct = "default"
tokenJSON, err := metadata.Get("instance/service-accounts/" + acct + "/token")
if err != nil {
return nil, err
var res struct {
AccessToken string `json:"access_token"`
ExpiresInSec int `json:"expires_in"`
TokenType string `json:"token_type"`
err = json.NewDecoder(strings.NewReader(tokenJSON)).Decode(&res)
if err != nil {
return nil, fmt.Errorf("oauth2/google: invalid token JSON from metadata: %v", err)
if res.ExpiresInSec == 0 || res.AccessToken == "" {
return nil, fmt.Errorf("oauth2/google: incomplete token received from metadata")
return &oauth2.Token{
AccessToken: res.AccessToken,
TokenType: res.TokenType,
Expiry: time.Now().Add(time.Duration(res.ExpiresInSec) * time.Second),
}, nil