fix(auth): don't try to detect default creds it opt configured (#10143)

Author: codyoss

auth/grpctransport/grpctransport.go

@@ -216,12 +216,16 @@ func dial(ctx context.Context, secure bool, opts *Options) (*grpc.ClientConn, er
 	// Authentication can only be sent when communicating over a secure connection.
 	if !opts.DisableAuthentication {
 		metadata := opts.Metadata
-		creds, err := credentials.DetectDefault(opts.resolveDetectOptions())
-		if err != nil {
-			return nil, err
-		}
+
+		var creds *auth.Credentials
 		if opts.Credentials != nil {
 			creds = opts.Credentials
+		} else {
+			var err error
+			creds, err = credentials.DetectDefault(opts.resolveDetectOptions())
+			if err != nil {
+				return nil, err
+			}
 		}
 
 		qp, err := creds.QuotaProjectID(ctx)

auth/httptransport/transport.go

@@ -58,9 +58,15 @@ func newTransport(base http.RoundTripper, opts *Options) (http.RoundTripper, err
 			Key:       opts.APIKey,
 		}
 	default:
-		creds, err := credentials.DetectDefault(opts.resolveDetectOptions())
-		if err != nil {
-			return nil, err
+		var creds *auth.Credentials
+		if opts.Credentials != nil {
+			creds = opts.Credentials
+		} else {
+			var err error
+			creds, err = credentials.DetectDefault(opts.resolveDetectOptions())
+			if err != nil {
+				return nil, err
+			}
 		}
 		qp, err := creds.QuotaProjectID(context.Background())
 		if err != nil {
@@ -72,10 +78,6 @@ func newTransport(base http.RoundTripper, opts *Options) (http.RoundTripper, err
 			}
 			headers.Set(quotaProjectHeaderKey, qp)
 		}
-
-		if opts.Credentials != nil {
-			creds = opts.Credentials
-		}
 		creds.TokenProvider = auth.NewCachedTokenProvider(creds.TokenProvider, nil)
 		trans = &authTransport{
 			base:                 trans,