fix: allow default credentials to work for GCP

cmd/tusd/cli/composer.go

@@ -80,7 +80,7 @@ func CreateComposer() {
 		// GCS_SERVICE_ACCOUNT_FILE environment variable.
 		gcsSAF := os.Getenv("GCS_SERVICE_ACCOUNT_FILE")
 		if gcsSAF == "" {
-			stderr.Fatalf("No service account file provided for Google Cloud Storage using the GCS_SERVICE_ACCOUNT_FILE environment variable.\n")
+			stdout.Printf("Attempting to use default GCS credentials because no GCS_SERVICE_ACCOUNT_FILE env var was provided\n")
 		}
 
 		service, err := gcsstore.NewGCSService(gcsSAF)

go.mod

@@ -3,8 +3,9 @@ module github.com/tus/tusd/v2
 // Specify the Go version needed for the Heroku deployment
 // See https://github.com/heroku/heroku-buildpack-go#go-module-specifics
 // +heroku goVersion go1.22
-go 1.21.0
-toolchain go1.22.7
+go 1.22.1
+
+toolchain go1.23.1
 
 require (
 	cloud.google.com/go/storage v1.43.0

pkg/gcsstore/gcsservice.go

@@ -81,7 +81,12 @@ type GCSService struct {
 // NewGCSService returns a GCSService object given a GCloud service account file path.
 func NewGCSService(filename string) (*GCSService, error) {
 	ctx := context.Background()
-	client, err := storage.NewClient(ctx, option.WithCredentialsFile(filename))
+	var opts []option.ClientOption
+	if filename != "" {
+		opts = append(opts, option.WithCredentialsFile(filename))
+	}
+	client, err := storage.NewClient(ctx, opts...)
+
 	if err != nil {
 		return nil, err
 	}