implement identity provider and built-in oauth server

Signed-off-by: hongming <talonwan@yunify.com>

pkg/apiserver/authentication/identityprovider/identity_provider.go

@@ -0,0 +1,25 @@
+/*
+ *
+ * Copyright 2020 The KubeSphere Authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * /
+ */
+
+package identityprovider
+
+import "k8s.io/apiserver/pkg/authentication/user"
+
+type OAuth2Interface interface {
+	IdentityExchange(code string) (user.Info, error)
+}