You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: apiserver.go
    path of file: ./repos/gardener/pkg/apiserver
    
    the code of the file until where you have to start completion: // Copyright 2018 SAP SE or an SAP affiliate company. All rights reserved. This file is licensed under the Apache Software License, v. 2 except as noted otherwise in the LICENSE file
//
// 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 WARR
    
func (o *ExtraOptions) AddFlags(fs *pflag.FlagSet) {
	fs.StringVar(&o.ClusterIdentity, "cluster-identity", o.ClusterIdentity, "This flag is used for specifying the identity of the Garden cluster")
	fs.DurationVar(&o.AdminKubeconfigMaxExpiration, "shoot-admin-kubeconfig-max-expiration", time.Hour*24, "The maximum validity duration of a credential requested to a Shoot by an AdminKubeconfigRequest. If an otherwise valid AdminKubeconfigRequest with a validity duration larger than this value is requested, a credential will be issued with a validity duration of this value.")
	fs.DurationVar(&o.ViewerKubeconfigMaxExpiration, "shoot-viewer-kubeconfig-max-expiration", time.Hour*24, "The maximum validity duration of a credential requested to a Shoot by an ViewerKubeconfigRequest. If an otherwise valid ViewerKubeconfigRequest with a validity duration larger than this value is requested, a credential will be issued with a validity duration of this value.")
	fs.DurationVar(&o.CredentialsRotationInterval, "shoot-credentials-rotation-interval", time.Hour*24*90, "The duration after the initial shoot creation or the last credentials rotation when a client warning for the next credentials rotation is issued.")

	fs.StringVar(&o.LogLevel, "log-level", "info", "The level/severity for the logs. Must be one of [info,debug,error]")
	fs.StringVar(&o.LogFormat, "log-format", "json", "The format for the logs. Must be one of [json,text]")
}