From 7ba02993703dac101f1673401fd5297b1d32aff7 Mon Sep 17 00:00:00 2001
From: line1029 <line1029@naver.com>
Date: Thu, 15 Jan 2026 23:58:47 +0900
Subject: [PATCH] feat(gcs): add support for application default credentials
 (ADC)

Allows GCS initialization without explicit credentials to support ADC. Fixes #18.
---
 oss/gcsblob/gcs.go | 23 ++++++++++++++++-------
 oss/oss.go         |  4 ++--
 2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/oss/gcsblob/gcs.go b/oss/gcsblob/gcs.go
index 43a8eb4..08e7be6 100644
--- a/oss/gcsblob/gcs.go
+++ b/oss/gcsblob/gcs.go
@@ -29,13 +29,22 @@ func NewGoogleCloudStorage(args oss.OSSArgs) (oss.OSS, error) {
 	ctx := context.Background()
 	bucket := args.GoogleCloudStorage.Bucket
 	credentialsB64 := args.GoogleCloudStorage.CredentialsB64
-	credentials, err := base64.StdEncoding.DecodeString(credentialsB64)
-	if err != nil {
-		return nil, oss.ErrProviderInit.WithError(err).WithDetail("credentials must be a base64 encoded string")
-	}
-	client, err := storage.NewClient(ctx, option.WithCredentialsJSON(credentials))
-	if err != nil {
-		return nil, oss.ErrProviderInit.WithError(err)
+
+	var client *storage.Client
+	if credentialsB64 == "" {
+		client, err = storage.NewClient(ctx)
+		if err != nil {
+			return nil, oss.ErrProviderInit.WithError(err).WithDetail("failed to initialize GCS client with ADC")
+		}
+	} else {
+		credentials, err := base64.StdEncoding.DecodeString(credentialsB64)
+		if err != nil {
+			return nil, oss.ErrProviderInit.WithError(err).WithDetail("credentials must be a base64 encoded string")
+		}
+		client, err = storage.NewClient(ctx, option.WithCredentialsJSON(credentials))
+		if err != nil {
+			return nil, oss.ErrProviderInit.WithError(err)
+		}
 	}
 	return &GoogleCloudStorage{
 		bucket: bucket,
diff --git a/oss/oss.go b/oss/oss.go
index c7aaa80..376cd20 100644
--- a/oss/oss.go
+++ b/oss/oss.go
@@ -143,8 +143,8 @@ type GoogleCloudStorage struct {
 }
 
 func (g *GoogleCloudStorage) Validate() error {
-	if g.Bucket == "" || g.CredentialsB64 == "" {
-		msg := fmt.Sprintf("bucket and credentials cannot be empty.")
+	if g.Bucket == "" {
+		msg := fmt.Sprintf("bucket cannot be empty.")
 		return ErrArgumentInvalid.WithDetail(msg)
 	}
 	return nil