feat: add multiple authentication methods, token and oidc.

token is the current token comparison, and oidc generates oidc token using client-credentials flow. in addition - add ping verification using the same method

vendor/golang.org/x/oauth2/internal/doc.go

@@ -0,0 +1,6 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package internal contains support packages for oauth2 package.
+package internal