credentials/google: introduce a new API NewComputeEngineCredsWithOptions

credentials/google/google.go

@@ -76,6 +76,26 @@ func NewComputeEngineCredentials() credentials.Bundle {
 	return bundle
 }
 
+// NewComputeEngineCredsWithPerRPC returns a credentials bundle that is configured to work
+// with google services. This API must only be used when running on GCE.
+//
+// This API is experimental.
+func NewComputeEngineCredsWithPerRPC(cc credentials.PerRPCCredentials) credentials.Bundle {
+	c := &creds{
+		newPerRPCCreds: func() credentials.PerRPCCredentials {
+			if cc != nil {
+				return cc
+			}
+			return oauth.NewComputeEngine()
+		},
+	}
+	bundle, err := c.NewWithMode(internal.CredsBundleModeFallback)
+	if err != nil {
+		logger.Warningf("compute engine creds with per rpc: failed to create new creds: %v", err)
+	}
+	return bundle
+}
+
 // creds implements credentials.Bundle.
 type creds struct {
 	// Supported modes are defined in internal/internal.go.

credentials/google/google_test.go

@@ -76,8 +76,9 @@ func overrideNewCredsFuncs() func() {
 func TestClientHandshakeBasedOnClusterName(t *testing.T) {
 	defer overrideNewCredsFuncs()()
 	for bundleTyp, tc := range map[string]credentials.Bundle{
-		"defaultCreds": NewDefaultCredentials(),
-		"computeCreds": NewComputeEngineCredentials(),
+		"defaultCreds":       NewDefaultCredentials(),
+		"computeCreds":       NewComputeEngineCredentials(),
+		"computeCredsPerRPC": NewComputeEngineCredsWithPerRPC(nil),
 	} {
 		tests := []struct {
 			name    string