Automatically load Google auth

This change removes the hardcoded Google auth mechanism for the GCS
backend, instead using Google's provided client library to discover and
generate credential material.

Google recommend that client libraries use their common auth mechanism
in order to authorise requests against Google services. Doing so means
you automatically support various types of authentication, from the
standard GOOGLE_APPLICATION_CREDENTIALS environment variable to making
use of Google's metadata API if running within Google Container Engine.

cmd/restic/global.go

@@ -440,18 +440,6 @@ func parseConfig(loc location.Location, opts options.Options) (interface{}, erro
 			cfg.ProjectID = os.Getenv("GOOGLE_PROJECT_ID")
 		}
 
-		if cfg.JSONKeyPath == "" {
-			if path := os.Getenv("GOOGLE_APPLICATION_CREDENTIALS"); path != "" {
-				// Check read access
-				if _, err := ioutil.ReadFile(path); err != nil {
-					return nil, errors.Fatalf("Failed to read google credential from file %v: %v", path, err)
-				}
-				cfg.JSONKeyPath = path
-			} else {
-				return nil, errors.Fatal("No credential file path is set")
-			}
-		}
-
 		if err := opts.Apply(loc.Scheme, &cfg); err != nil {
 			return nil, err
 		}

internal/backend/gs/config.go

@@ -8,11 +8,11 @@ import (
 	"github.com/restic/restic/internal/options"
 )
 
-// Config contains all configuration necessary to connect to a Google Cloud
+// Config contains all configuration necessary to connect to a Google Cloud Storage
-// Storage bucket.
+// bucket. We use Google's default application credentials to acquire an access token, so
+// we don't require that calling code supply any authentication material here.
 type Config struct {
 	ProjectID string
-	JSONKeyPath string
 	Bucket    string
 	Prefix    string
 

internal/backend/gs/gs.go

@@ -15,9 +15,6 @@ import (
 	"github.com/restic/restic/internal/debug"
 	"github.com/restic/restic/internal/restic"
 
-	"io/ioutil"
-
-	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/google"
 	"google.golang.org/api/googleapi"
 	storage "google.golang.org/api/storage/v1"
@@ -43,30 +40,12 @@ type Backend struct {
 // Ensure that *Backend implements restic.Backend.
 var _ restic.Backend = &Backend{}
 
-func getStorageService(jsonKeyPath string, rt http.RoundTripper) (*storage.Service, error) {
+func getStorageService() (*storage.Service, error) {
-
+	client, err := google.DefaultClient(context.TODO(), storage.DevstorageReadWriteScope)
-	raw, err := ioutil.ReadFile(jsonKeyPath)
-	if err != nil {
-		return nil, errors.Wrap(err, "ReadFile")
-	}
-
-	conf, err := google.JWTConfigFromJSON(raw, storage.DevstorageReadWriteScope)
 	if err != nil {
 		return nil, err
 	}
 
-	// create a new HTTP client
-	httpClient := &http.Client{
-		Transport: rt,
-	}
-
-	// create a now context with the HTTP client stored at the oauth2.HTTPClient key
-	ctx := context.WithValue(context.Background(), oauth2.HTTPClient, httpClient)
-
-	// then pass this context to Client(), which returns a new HTTP client
-	client := conf.Client(ctx)
-
-	// that we can then pass to New()
 	service, err := storage.New(client)
 	if err != nil {
 		return nil, err
@@ -80,7 +59,7 @@ const defaultListMaxItems = 1000
 func open(cfg Config, rt http.RoundTripper) (*Backend, error) {
 	debug.Log("open, config %#v", cfg)
 
-	service, err := getStorageService(cfg.JSONKeyPath, rt)
+	service, err := getStorageService()
 	if err != nil {
 		return nil, errors.Wrap(err, "getStorageService")
 	}

internal/backend/gs/gs_test.go

@@ -34,7 +34,6 @@ func newGSTestSuite(t testing.TB) *test.Suite {
 
 			cfg := gscfg.(gs.Config)
 			cfg.ProjectID = os.Getenv("RESTIC_TEST_GS_PROJECT_ID")
-			cfg.JSONKeyPath = os.Getenv("RESTIC_TEST_GS_APPLICATION_CREDENTIALS")
 			cfg.Prefix = fmt.Sprintf("test-%d", time.Now().UnixNano())
 			return cfg, nil
 		},
@@ -88,8 +87,8 @@ func TestBackendGS(t *testing.T) {
 	}()
 
 	vars := []string{
+		"GOOGLE_APPLICATION_CREDENTIALS",
 		"RESTIC_TEST_GS_PROJECT_ID",
-		"RESTIC_TEST_GS_APPLICATION_CREDENTIALS",
 		"RESTIC_TEST_GS_REPOSITORY",
 	}
 
@@ -106,8 +105,8 @@ func TestBackendGS(t *testing.T) {
 
 func BenchmarkBackendGS(t *testing.B) {
 	vars := []string{
+		"GOOGLE_APPLICATION_CREDENTIALS",
 		"RESTIC_TEST_GS_PROJECT_ID",
-		"RESTIC_TEST_GS_APPLICATION_CREDENTIALS",
 		"RESTIC_TEST_GS_REPOSITORY",
 	}
 

run_integration_tests.go

@@ -183,7 +183,7 @@ func (env *TravisEnvironment) RunTests() error {
 
 	env.env["GOPATH"] = os.Getenv("GOPATH")
 	if env.gcsCredentialsFile != "" {
-		env.env["RESTIC_TEST_GS_APPLICATION_CREDENTIALS"] = env.gcsCredentialsFile
+		env.env["GOOGLE_APPLICATION_CREDENTIALS"] = env.gcsCredentialsFile
 	}
 
 	// ensure that the following tests cannot be silently skipped on Travis