failed to access the gcs when use custom http client

[Leavrth]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. restore data from gcs

2. What did you expect to see? (Required)

success

3. What did you see instead (Required)

failed

Error 401: Anonymous caller does not have storage.objects.list access to the Google Cloud Storage bucket. Permission 'storage.objects.list' denied on resource (or it may not exist).

4. What is your TiDB version? (Required)

master, v6.5.4

[Leavrth]

The gcs credential is saved in the Transport of http.Client. So we need to support the HTTPClient with the credential:
https://github.com/googleapis/google-api-go-client/blob/f79df4875aea4520e4aff5c5ebceb9e01b7b60a2/transport/http/dial.go#L42

[YuJuncen]

There is another solution for this, we can wrap the transport provided in the users' HTTPClient if there are:

diff --git a/br/pkg/storage/gcs.go b/br/pkg/storage/gcs.go
index f32d4344d9..468b03dda1 100644
--- a/br/pkg/storage/gcs.go
+++ b/br/pkg/storage/gcs.go
@@ -20,6 +20,8 @@ import (
        "golang.org/x/oauth2/google"
        "google.golang.org/api/iterator"
        "google.golang.org/api/option"
+
+       htransport "google.golang.org/api/transport/http"
 )
 
 const (
@@ -292,11 +294,16 @@ func NewGCSStorage(ctx context.Context, gcs *backuppb.GCS, opts *ExternalStorage
                        clientOps = append(clientOps, option.WithCredentialsJSON([]byte(gcs.GetCredentialsBlob())))
                }
        }
-
        if gcs.Endpoint != "" {
                clientOps = append(clientOps, option.WithEndpoint(gcs.Endpoint))
        }
        if opts.HTTPClient != nil {
+               var err error
+               opts.HTTPClient.Transport, err = htransport.NewTransport(ctx, opts.HTTPClient.Transport,
+                       append(clientOps, option.WithScopes(storage.ScopeFullControl, "https://www.googleapis.com/auth/cloud-platform"))...)
+               if err != nil {
+                       return nil, errors.Trace(err)
+               }
                clientOps = append(clientOps, option.WithHTTPClient(opts.HTTPClient))
        }
        client, err := storage.NewClient(ctx, clientOps...)
diff --git a/br/pkg/storage/gcs_test.go b/br/pkg/storage/gcs_test.go
index c6d7e14b80..31c68c5ebc 100644