^^&&^^

Edit File: UpdateMetadataInterface.php

<?php
/*
 * Copyright 2020 Google LLC
 *
 * 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.
 */

namespace Google\Auth;

/**
 * Describes a Credentials object which supports updating request metadata
 * (request headers).
 */
interface UpdateMetadataInterface
{
    const AUTH_METADATA_KEY = 'authorization';

/**
     * Updates metadata with the authorization token.
     *
     * @param array $metadata metadata hashmap
     * @param string $authUri optional auth uri
     * @param callable $httpHandler callback which delivers psr7 request
     * @return array updated metadata hashmap
     */
    public function updateMetadata(
        $metadata,
        $authUri = null,
        callable $httpHandler = null
    );
}