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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\Middleware;

use Google\Auth\FetchAuthTokenInterface;

use Psr\Http\Message\RequestInterface;

/**

 * AuthTokenMiddleware is a Guzzle Middleware that adds an Authorization header

 * provided by an object implementing FetchAuthTokenInterface.

 *

 * The FetchAuthTokenInterface#fetchAuthToken is used to obtain a hash; one of

 * the values value in that hash is added as the authorization header.

 *

 * Requests will be accessed with the authorization header:

 *

 * 'Authorization' 'Bearer <value of auth_token>'

 */

class AuthTokenMiddleware

{

    /**

     * @var callback

     */

    private $httpHandler;

    /**

     * @var FetchAuthTokenInterface

     */

    private $fetcher;

    /**

     * @var callable

     */

    private $tokenCallback;

    /**

     * Creates a new AuthTokenMiddleware.

     *

     * @param FetchAuthTokenInterface $fetcher is used to fetch the auth token

     * @param callable $httpHandler (optional) callback which delivers psr7 request

     * @param callable $tokenCallback (optional) function to be called when a new token is fetched.

     */

    public function __construct(

        FetchAuthTokenInterface $fetcher,

        callable $httpHandler = null,

        callable $tokenCallback = null

    ) {

        $this->fetcher = $fetcher;

        $this->httpHandler = $httpHandler;

        $this->tokenCallback = $tokenCallback;

    }

    /**

     * Updates the request with an Authorization header when auth is 'google_auth'.

     *

     *   use Google\Auth\Middleware\AuthTokenMiddleware;

     *   use Google\Auth\OAuth2;

     *   use GuzzleHttp\Client;

     *   use GuzzleHttp\HandlerStack;

     *

     *   $config = [..<oauth config param>.];

     *   $oauth2 = new OAuth2($config)

     *   $middleware = new AuthTokenMiddleware($oauth2);

     *   $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');

     *

     * @param callable $handler

     *

     * @return \Closure

     */

    public function __invoke(callable $handler)

    {

        return function (RequestInterface $request, array $options) use ($handler) {

            // Requests using "auth"="google_auth" will be authorized.

            if (!isset($options['auth']) || $options['auth'] !== 'google_auth') {

                return $handler($request, $options);

            }

            $request = $request->withHeader('Authorization', 'Bearer ' . $this->fetchToken());

            return $handler($request, $options);

        };

    }

    /**

     * Call fetcher to fetch the token.

     *

     * @return string

     */

    private function fetchToken()

    {

        $auth_tokens = $this->fetcher->fetchAuthToken($this->httpHandler);

        if (array_key_exists('access_token', $auth_tokens)) {

            // notify the callback if applicable

            if ($this->tokenCallback) {

                call_user_func($this->tokenCallback, $this->fetcher->getCacheKey(), $auth_tokens['access_token']);

            }

            return $auth_tokens['access_token'];

        }

    }

}