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<?php

/*

 * Copyright 2015 Google Inc.

 *

 * 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;

use DomainException;

use Google\Auth\Credentials\AppIdentityCredentials;

use Google\Auth\Credentials\GCECredentials;

use Google\Auth\Middleware\AuthTokenMiddleware;

use Google\Auth\Subscriber\AuthTokenSubscriber;

use Psr\Cache\CacheItemPoolInterface;

/**

 * ApplicationDefaultCredentials obtains the default credentials for

 * authorizing a request to a Google service.

 *

 * Application Default Credentials are described here:

 * https://developers.google.com/accounts/docs/application-default-credentials

 *

 * This class implements the search for the application default credentials as

 * described in the link.

 *

 * It provides three factory methods:

 * - #get returns the computed credentials object

 * - #getSubscriber returns an AuthTokenSubscriber built from the credentials object

 * - #getMiddleware returns an AuthTokenMiddleware built from the credentials object

 *

 * This allows it to be used as follows with GuzzleHttp\Client:

 *

 *   use Google\Auth\ApplicationDefaultCredentials;

 *   use GuzzleHttp\Client;

 *   use GuzzleHttp\HandlerStack;

 *

 *   $middleware = ApplicationDefaultCredentials::getMiddleware(

 *       'https://www.googleapis.com/auth/taskqueue'

 *   );

 *   $stack = HandlerStack::create();

 *   $stack->push($middleware);

 *

 *   $client = new Client([

 *       'handler' => $stack,

 *       'base_uri' => 'https://www.googleapis.com/taskqueue/v1beta2/projects/',

 *       'auth' => 'google_auth' // authorize all requests

 *   ]);

 *

 *   $res = $client->get('myproject/taskqueues/myqueue');

 */

class ApplicationDefaultCredentials

{

    /**

     * Obtains an AuthTokenSubscriber that uses the default FetchAuthTokenInterface

     * implementation to use in this environment.

     *

     * If supplied, $scope is used to in creating the credentials instance if

     * this does not fallback to the compute engine defaults.

     *

     * @param string|array scope the scope of the access request, expressed

     *   either as an Array or as a space-delimited String.

     * @param callable $httpHandler callback which delivers psr7 request

     * @param array $cacheConfig configuration for the cache when it's present

     * @param CacheItemPoolInterface $cache an implementation of CacheItemPoolInterface

     *

     * @return AuthTokenSubscriber

     *

     * @throws DomainException if no implementation can be obtained.

     */

    public static function getSubscriber(

        $scope = null,

        callable $httpHandler = null,

        array $cacheConfig = null,

        CacheItemPoolInterface $cache = null

    ) {

        $creds = self::getCredentials($scope, $httpHandler, $cacheConfig, $cache);

        return new AuthTokenSubscriber($creds, $cacheConfig);

    }

    /**

     * Obtains an AuthTokenMiddleware that uses the default FetchAuthTokenInterface

     * implementation to use in this environment.

     *

     * If supplied, $scope is used to in creating the credentials instance if

     * this does not fallback to the compute engine defaults.

     *

     * @param string|array scope the scope of the access request, expressed

     *   either as an Array or as a space-delimited String.

     * @param callable $httpHandler callback which delivers psr7 request

     * @param array $cacheConfig configuration for the cache when it's present

     * @param CacheItemPoolInterface $cache

     *

     * @return AuthTokenMiddleware

     *

     * @throws DomainException if no implementation can be obtained.

     */

    public static function getMiddleware(

        $scope = null,

        callable $httpHandler = null,

        array $cacheConfig = null,

        CacheItemPoolInterface $cache = null

    ) {

        $creds = self::getCredentials($scope, $httpHandler, $cacheConfig, $cache);

        return new AuthTokenMiddleware($creds, $cacheConfig);

    }

    /**

     * Obtains the default FetchAuthTokenInterface implementation to use

     * in this environment.

     *

     * If supplied, $scope is used to in creating the credentials instance if

     * this does not fallback to the Compute Engine defaults.

     *

     * @param string|array scope the scope of the access request, expressed

     *   either as an Array or as a space-delimited String.

     * @param callable $httpHandler callback which delivers psr7 request

     * @param array $cacheConfig configuration for the cache when it's present

     * @param CacheItemPoolInterface $cache

     *

     * @return CredentialsLoader

     *

     * @throws DomainException if no implementation can be obtained.

     */

    public static function getCredentials(

        $scope = null,

        callable $httpHandler = null,

        array $cacheConfig = null,

        CacheItemPoolInterface $cache = null

    ) {

        $creds = null;

        $jsonKey = CredentialsLoader::fromEnv()

            ?: CredentialsLoader::fromWellKnownFile();

        if (!is_null($jsonKey)) {

            $creds = CredentialsLoader::makeCredentials($scope, $jsonKey);

        } elseif (AppIdentityCredentials::onAppEngine() && !GCECredentials::onAppEngineFlexible()) {

            $creds = new AppIdentityCredentials($scope);

        } elseif (GCECredentials::onGce($httpHandler)) {

            $creds = new GCECredentials();

        }

        if (is_null($creds)) {

            throw new \DomainException(self::notFound());

        }

        if (!is_null($cache)) {

            $creds = new FetchAuthTokenCache($creds, $cacheConfig, $cache);

        }

        return $creds;

    }

    private static function notFound()

    {

        $msg = 'Could not load the default credentials. Browse to ';

        $msg .= 'https://developers.google.com';

        $msg .= '/accounts/docs/application-default-credentials';

        $msg .= ' for more information';

        return $msg;

    }

}