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// Copyright 2015 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
import (
"encoding/json"
"fmt"
"io/ioutil"
"net/http"
"os"
"path/filepath"
"runtime"
"cloud.google.com/go/compute/metadata"
"golang.org/x/net/context"
"golang.org/x/oauth2"
)
// DefaultCredentials holds "Application Default Credentials".
// For more details, see:
// https://developers.google.com/accounts/docs/application-default-credentials
type DefaultCredentials struct {
ProjectID string // may be empty
TokenSource oauth2.TokenSource
}
// DefaultClient returns an HTTP Client that uses the
// DefaultTokenSource to obtain authentication credentials.
func DefaultClient(ctx context.Context, scope ...string) (*http.Client, error) {
ts, err := DefaultTokenSource(ctx, scope...)
if err != nil {
return nil, err
}
return oauth2.NewClient(ctx, ts), nil
}
// DefaultTokenSource returns the token source for
// "Application Default Credentials".
// It is a shortcut for FindDefaultCredentials(ctx, scope).TokenSource.
func DefaultTokenSource(ctx context.Context, scope ...string) (oauth2.TokenSource, error) {
creds, err := FindDefaultCredentials(ctx, scope...)
if err != nil {
return nil, err
}
return creds.TokenSource, nil
}
// FindDefaultCredentials searches for "Application Default Credentials".
//
// It looks for credentials in the following places,
// preferring the first location found:
//
// 1. A JSON file whose path is specified by the
// GOOGLE_APPLICATION_CREDENTIALS environment variable.
// 2. A JSON file in a location known to the gcloud command-line tool.
// On Windows, this is %APPDATA%/gcloud/application_default_credentials.json.
// On other systems, $HOME/.config/gcloud/application_default_credentials.json.
// 3. On Google App Engine it uses the appengine.AccessToken function.
// 4. On Google Compute Engine and Google App Engine Managed VMs, it fetches
// credentials from the metadata server.
// (In this final case any provided scopes are ignored.)
func FindDefaultCredentials(ctx context.Context, scope ...string) (*DefaultCredentials, error) {
// First, try the environment variable.
const envVar = "GOOGLE_APPLICATION_CREDENTIALS"
if filename := os.Getenv(envVar); filename != "" {
creds, err := readCredentialsFile(ctx, filename, scope)
if err != nil {
return nil, fmt.Errorf("google: error getting credentials using %v environment variable: %v", envVar, err)
}
return creds, nil
}
// Second, try a well-known file.
filename := wellKnownFile()
if creds, err := readCredentialsFile(ctx, filename, scope); err == nil {
return creds, nil
} else if !os.IsNotExist(err) {
return nil, fmt.Errorf("google: error getting credentials using well-known file (%v): %v", filename, err)
}
// Third, if we're on Google App Engine use those credentials.
if appengineTokenFunc != nil && !appengineFlex {
return &DefaultCredentials{
ProjectID: appengineAppIDFunc(ctx),
TokenSource: AppEngineTokenSource(ctx, scope...),
}, nil
}
// Fourth, if we're on Google Compute Engine use the metadata server.
if metadata.OnGCE() {
id, _ := metadata.ProjectID()
return &DefaultCredentials{
ProjectID: id,
TokenSource: ComputeTokenSource(""),
}, nil
}
// None are found; return helpful error.
const url = "https://developers.google.com/accounts/docs/application-default-credentials"
return nil, fmt.Errorf("google: could not find default credentials. See %v for more information.", url)
}
func wellKnownFile() string {
const f = "application_default_credentials.json"
if runtime.GOOS == "windows" {
return filepath.Join(os.Getenv("APPDATA"), "gcloud", f)
}
return filepath.Join(guessUnixHomeDir(), ".config", "gcloud", f)
}
func readCredentialsFile(ctx context.Context, filename string, scopes []string) (*DefaultCredentials, error) {
b, err := ioutil.ReadFile(filename)
if err != nil {
return nil, err
}
var f credentialsFile
if err := json.Unmarshal(b, &f); err != nil {
return nil, err
}
ts, err := f.tokenSource(ctx, append([]string(nil), scopes...))
if err != nil {
return nil, err
}
return &DefaultCredentials{
ProjectID: f.ProjectID,
TokenSource: ts,
}, nil
}
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