<?php
/*
 * Copyright 2008 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.
 */

/**
 * Authentication class that deals with the OAuth 2 web-server authentication flow
 *
 * @author Chris Chabot <chabotc@google.com>
 * @author Chirag Shah <chirags@google.com>
 *
 */
class Google_Auth_OAuth2 extends Google_Auth_Abstract {

    const OAUTH2_REVOKE_URI = 'https://accounts.google.com/o/oauth2/revoke';
    const OAUTH2_TOKEN_URI = 'https://accounts.google.com/o/oauth2/token';
    const OAUTH2_AUTH_URL = 'https://accounts.google.com/o/oauth2/auth';
    const CLOCK_SKEW_SECS = 300; // five minutes in seconds
    const AUTH_TOKEN_LIFETIME_SECS = 300; // five minutes in seconds
    const MAX_TOKEN_LIFETIME_SECS = 86400; // one day in seconds
    const OAUTH2_ISSUER = 'accounts.google.com';

    /** @var Google_Auth_AssertionCredentials $assertionCredentials */
    private $assertionCredentials;

    /**
     * @var string The state parameters for CSRF and other forgery protection.
     */
    private $state;

    /**
     * @var array The token bundle.
     */
    private $token = array();

    /**
     * @var Google_Client the base client
     */
    private $client;

    /**
     * Instantiates the class, but does not initiate the login flow, leaving it
     * to the discretion of the caller.
     */
    public function __construct(Google_Client $client) {
        $this->client = $client;
    }

    /**
     * Perform an authenticated / signed apiHttpRequest.
     * This function takes the apiHttpRequest, calls apiAuth->sign on it
     * (which can modify the request in what ever way fits the auth mechanism)
     * and then calls apiCurlIO::makeRequest on the signed request
     *
     * @param Google_Http_Request $request
     *
     * @return Google_Http_Request The resulting HTTP response including the
     * responseHttpCode, responseHeaders and responseBody.
     */
    public function authenticatedRequest(Google_Http_Request $request) {
        $request = $this->sign($request);

        return $this->client->getIo()
                            ->makeRequest($request);
    }

    /**
     * @param string $code
     *
     * @throws Google_Auth_Exception
     * @return string
     */
    public function authenticate($code) {
        if (strlen($code) == 0) {
            throw new Google_Auth_Exception("Invalid code");
        }

        // We got here from the redirect from a successful authorization grant,
        // fetch the access token
        $request = new Google_Http_Request(self::OAUTH2_TOKEN_URI, 'POST', array(), array(
                'code'          => $code,
                'grant_type'    => 'authorization_code',
                'redirect_uri'  => $this->client->getClassConfig($this, 'redirect_uri'),
                'client_id'     => $this->client->getClassConfig($this, 'client_id'),
                'client_secret' => $this->client->getClassConfig($this, 'client_secret')
            ));
        $request->disableGzip();
        $response = $this->client->getIo()
                                 ->makeRequest($request);

        if ($response->getResponseHttpCode() == 200) {
            $this->setAccessToken($response->getResponseBody());
            $this->token['created'] = time();

            return $this->getAccessToken();
        } else {
            $decodedResponse = json_decode($response->getResponseBody(), true);
            if ($decodedResponse != null && $decodedResponse['error']) {
                $errorText = $decodedResponse['error'];
                if (isset($decodedResponse['error_description'])) {
                    $errorText .= ": " . $decodedResponse['error_description'];
                }
            }
            throw new Google_Auth_Exception(sprintf("Error fetching OAuth2 access token, message: '%s'", $errorText), $response->getResponseHttpCode());
        }
    }

    /**
     * Create a URL to obtain user authorization.
     * The authorization endpoint allows the user to first
     * authenticate, and then grant/deny the access request.
     *
     * @param string $scope The scope is expressed as a list of space-delimited strings.
     *
     * @return string
     */
    public function createAuthUrl($scope) {
        $params = array(
            'response_type' => 'code',
            'redirect_uri'  => $this->client->getClassConfig($this, 'redirect_uri'),
            'client_id'     => $this->client->getClassConfig($this, 'client_id'),
            'scope'         => $scope,
            'access_type'   => $this->client->getClassConfig($this, 'access_type'),
        );

        // Prefer prompt to approval prompt.
        if ($this->client->getClassConfig($this, 'prompt')) {
            $params = $this->maybeAddParam($params, 'prompt');
        } else {
            $params = $this->maybeAddParam($params, 'approval_prompt');
        }
        $params = $this->maybeAddParam($params, 'login_hint');
        $params = $this->maybeAddParam($params, 'hd');
        $params = $this->maybeAddParam($params, 'openid.realm');
        $params = $this->maybeAddParam($params, 'include_granted_scopes');

        // If the list of scopes contains plus.login, add request_visible_actions
        // to auth URL.
        $rva = $this->client->getClassConfig($this, 'request_visible_actions');
        if (strpos($scope, 'plus.login') && strlen($rva) > 0) {
            $params['request_visible_actions'] = $rva;
        }

        if (isset($this->state)) {
            $params['state'] = $this->state;
        }

        return self::OAUTH2_AUTH_URL . "?" . http_build_query($params, '', '&');
    }

    /**
     * @param string $token
     *
     * @throws Google_Auth_Exception
     */
    public function setAccessToken($token) {
        $token = json_decode($token, true);
        if ($token == null) {
            throw new Google_Auth_Exception('Could not json decode the token');
        }
        if (!isset($token['access_token'])) {
            throw new Google_Auth_Exception("Invalid token format");
        }
        $this->token = $token;
    }

    public function getAccessToken() {
        return json_encode($this->token);
    }

    public function getRefreshToken() {
        if (array_key_exists('refresh_token', $this->token)) {
            return $this->token['refresh_token'];
        } else {
            return null;
        }
    }

    public function setState($state) {
        $this->state = $state;
    }

    public function setAssertionCredentials(Google_Auth_AssertionCredentials $creds) {
        $this->assertionCredentials = $creds;
    }

    /**
     * Include an accessToken in a given apiHttpRequest.
     *
     * @param Google_Http_Request $request
     *
     * @return Google_Http_Request
     * @throws Google_Auth_Exception
     */
    public function sign(Google_Http_Request $request) {
        // add the developer key to the request before signing it
        if ($this->client->getClassConfig($this, 'developer_key')) {
            $request->setQueryParam('key', $this->client->getClassConfig($this, 'developer_key'));
        }

        // Cannot sign the request without an OAuth access token.
        if (null == $this->token && null == $this->assertionCredentials) {
            return $request;
        }

        // Check if the token is set to expire in the next 30 seconds
        // (or has already expired).
        if ($this->isAccessTokenExpired()) {
            if ($this->assertionCredentials) {
                $this->refreshTokenWithAssertion();
            } else {
                $this->client->getLogger()
                             ->debug('OAuth2 access token expired');
                if (!array_key_exists('refresh_token', $this->token)) {
                    $error = "The OAuth 2.0 access token has expired," . " and a refresh token is not available. Refresh tokens" . " are not returned for responses that were auto-approved.";

                    $this->client->getLogger()
                                 ->error($error);
                    throw new Google_Auth_Exception($error);
                }
                $this->refreshToken($this->token['refresh_token']);
            }
        }

        $this->client->getLogger()
                     ->debug('OAuth2 authentication');

        // Add the OAuth2 header to the request
        $request->setRequestHeaders(array('Authorization' => 'Bearer ' . $this->token['access_token']));

        return $request;
    }

    /**
     * Fetches a fresh access token with the given refresh token.
     *
     * @param string $refreshToken
     *
     * @return void
     */
    public function refreshToken($refreshToken) {
        $this->refreshTokenRequest(array(
                'client_id'     => $this->client->getClassConfig($this, 'client_id'),
                'client_secret' => $this->client->getClassConfig($this, 'client_secret'),
                'refresh_token' => $refreshToken,
                'grant_type'    => 'refresh_token'
            ));
    }

    /**
     * Fetches a fresh access token with a given assertion token.
     *
     * @param Google_Auth_AssertionCredentials $assertionCredentials optional.
     *
     * @return void
     */
    public function refreshTokenWithAssertion($assertionCredentials = null) {
        if (!$assertionCredentials) {
            $assertionCredentials = $this->assertionCredentials;
        }

        $cacheKey = $assertionCredentials->getCacheKey();

        if ($cacheKey) {
            // We can check whether we have a token available in the
            // cache. If it is expired, we can retrieve a new one from
            // the assertion.
            $token = $this->client->getCache()
                                  ->get($cacheKey);
            if ($token) {
                $this->setAccessToken($token);
            }
            if (!$this->isAccessTokenExpired()) {
                return;
            }
        }

        $this->client->getLogger()
                     ->debug('OAuth2 access token expired');
        $this->refreshTokenRequest(array(
                'grant_type'     => 'assertion',
                'assertion_type' => $assertionCredentials->assertionType,
                'assertion'      => $assertionCredentials->generateAssertion(),
            ));

        if ($cacheKey) {
            // Attempt to cache the token.
            $this->client->getCache()
                         ->set($cacheKey, $this->getAccessToken());
        }
    }

    private function refreshTokenRequest($params) {
        if (isset($params['assertion'])) {
            $this->client->getLogger()
                         ->info('OAuth2 access token refresh with Signed JWT assertion grants.');
        } else {
            $this->client->getLogger()
                         ->info('OAuth2 access token refresh');
        }

        $http = new Google_Http_Request(self::OAUTH2_TOKEN_URI, 'POST', array(), $params);
        $http->disableGzip();
        $request = $this->client->getIo()
                                ->makeRequest($http);

        $code = $request->getResponseHttpCode();
        $body = $request->getResponseBody();
        if (200 == $code) {
            $token = json_decode($body, true);
            if ($token == null) {
                throw new Google_Auth_Exception("Could not json decode the access token");
            }

            if (!isset($token['access_token']) || !isset($token['expires_in'])) {
                throw new Google_Auth_Exception("Invalid token format");
            }

            if (isset($token['id_token'])) {
                $this->token['id_token'] = $token['id_token'];
            }
            $this->token['access_token'] = $token['access_token'];
            $this->token['expires_in']   = $token['expires_in'];
            $this->token['created']      = time();
        } else {
            throw new Google_Auth_Exception("Error refreshing the OAuth2 token, message: '$body'", $code);
        }
    }

    /**
     * Revoke an OAuth2 access token or refresh token. This method will revoke the current access
     * token, if a token isn't provided.
     *
     * @throws Google_Auth_Exception
     *
     * @param string|null $token The token (access token or a refresh token) that should be revoked.
     *
     * @return boolean Returns True if the revocation was successful, otherwise False.
     */
    public function revokeToken($token = null) {
        if (!$token) {
            if (!$this->token) {
                // Not initialized, no token to actually revoke
                return false;
            } elseif (array_key_exists('refresh_token', $this->token)) {
                $token = $this->token['refresh_token'];
            } else {
                $token = $this->token['access_token'];
            }
        }
        $request = new Google_Http_Request(self::OAUTH2_REVOKE_URI, 'POST', array(), "token=$token");
        $request->disableGzip();
        $response = $this->client->getIo()
                                 ->makeRequest($request);
        $code     = $response->getResponseHttpCode();
        if ($code == 200) {
            $this->token = null;

            return true;
        }

        return false;
    }

    /**
     * Returns if the access_token is expired.
     *
     * @return bool Returns True if the access_token is expired.
     */
    public function isAccessTokenExpired() {
        if (!$this->token || !isset($this->token['created'])) {
            return true;
        }

        // If the token is set to expire in the next 30 seconds.
        $expired = ($this->token['created'] + ($this->token['expires_in'] - 30)) < time();

        return $expired;
    }

    // Gets federated sign-on certificates to use for verifying identity tokens.
    // Returns certs as array structure, where keys are key ids, and values
    // are PEM encoded certificates.
    private function getFederatedSignOnCerts() {
        return $this->retrieveCertsFromLocation($this->client->getClassConfig($this, 'federated_signon_certs_url'));
    }

    /**
     * Retrieve and cache a certificates file.
     *
     * @param $url string location
     *
     * @throws Google_Auth_Exception
     * @return array certificates
     */
    public function retrieveCertsFromLocation($url) {
        // If we're retrieving a local file, just grab it.
        if ("http" != substr($url, 0, 4)) {
            $file = file_get_contents($url);
            if ($file) {
                return json_decode($file, true);
            } else {
                throw new Google_Auth_Exception("Failed to retrieve verification certificates: '" . $url . "'.");
            }
        }

        // This relies on makeRequest caching certificate responses.
        $request = $this->client->getIo()
                                ->makeRequest(new Google_Http_Request($url));
        if ($request->getResponseHttpCode() == 200) {
            $certs = json_decode($request->getResponseBody(), true);
            if ($certs) {
                return $certs;
            }
        }
        throw new Google_Auth_Exception("Failed to retrieve verification certificates: '" . $request->getResponseBody() . "'.", $request->getResponseHttpCode());
    }

    /**
     * Verifies an id token and returns the authenticated apiLoginTicket.
     * Throws an exception if the id token is not valid.
     * The audience parameter can be used to control which id tokens are
     * accepted.  By default, the id token must have been issued to this OAuth2 client.
     *
     * @param $id_token
     * @param $audience
     *
     * @return Google_Auth_LoginTicket
     */
    public function verifyIdToken($id_token = null, $audience = null) {
        if (!$id_token) {
            $id_token = $this->token['id_token'];
        }
        $certs = $this->getFederatedSignonCerts();
        if (!$audience) {
            $audience = $this->client->getClassConfig($this, 'client_id');
        }

        return $this->verifySignedJwtWithCerts($id_token, $certs, $audience, self::OAUTH2_ISSUER);
    }

    /**
     * Verifies the id token, returns the verified token contents.
     *
     * @param $jwt               string the token
     * @param $certs             array of certificates
     * @param $required_audience string the expected consumer of the token
     * @param [$issuer] the expected issues, defaults to Google
     * @param [$max_expiry] the max lifetime of a token, defaults to MAX_TOKEN_LIFETIME_SECS
     *
     * @throws Google_Auth_Exception
     * @return mixed token information if valid, false if not
     */
    public function verifySignedJwtWithCerts($jwt, $certs, $required_audience, $issuer = null, $max_expiry = null) {
        if (!$max_expiry) {
            // Set the maximum time we will accept a token for.
            $max_expiry = self::MAX_TOKEN_LIFETIME_SECS;
        }

        $segments = explode(".", $jwt);
        if (count($segments) != 3) {
            throw new Google_Auth_Exception("Wrong number of segments in token: $jwt");
        }
        $signed    = $segments[0] . "." . $segments[1];
        $signature = Google_Utils::urlSafeB64Decode($segments[2]);

        // Parse envelope.
        $envelope = json_decode(Google_Utils::urlSafeB64Decode($segments[0]), true);
        if (!$envelope) {
            throw new Google_Auth_Exception("Can't parse token envelope: " . $segments[0]);
        }

        // Parse token
        $json_body = Google_Utils::urlSafeB64Decode($segments[1]);
        $payload   = json_decode($json_body, true);
        if (!$payload) {
            throw new Google_Auth_Exception("Can't parse token payload: " . $segments[1]);
        }

        // Check signature
        $verified = false;
        foreach ($certs as $keyName => $pem) {
            $public_key = new Google_Verifier_Pem($pem);
            if ($public_key->verify($signed, $signature)) {
                $verified = true;
                break;
            }
        }

        if (!$verified) {
            throw new Google_Auth_Exception("Invalid token signature: $jwt");
        }

        // Check issued-at timestamp
        $iat = 0;
        if (array_key_exists("iat", $payload)) {
            $iat = $payload["iat"];
        }
        if (!$iat) {
            throw new Google_Auth_Exception("No issue time in token: $json_body");
        }
        $earliest = $iat - self::CLOCK_SKEW_SECS;

        // Check expiration timestamp
        $now = time();
        $exp = 0;
        if (array_key_exists("exp", $payload)) {
            $exp = $payload["exp"];
        }
        if (!$exp) {
            throw new Google_Auth_Exception("No expiration time in token: $json_body");
        }
        if ($exp >= $now + $max_expiry) {
            throw new Google_Auth_Exception(sprintf("Expiration time too far in future: %s", $json_body));
        }

        $latest = $exp + self::CLOCK_SKEW_SECS;
        if ($now < $earliest) {
            throw new Google_Auth_Exception(sprintf("Token used too early, %s < %s: %s", $now, $earliest, $json_body));
        }
        if ($now > $latest) {
            throw new Google_Auth_Exception(sprintf("Token used too late, %s > %s: %s", $now, $latest, $json_body));
        }

        $iss = $payload['iss'];
        if ($issuer && $iss != $issuer) {
            throw new Google_Auth_Exception(sprintf("Invalid issuer, %s != %s: %s", $iss, $issuer, $json_body));
        }

        // Check audience
        $aud = $payload["aud"];
        if ($aud != $required_audience) {
            throw new Google_Auth_Exception(sprintf("Wrong recipient, %s != %s:", $aud, $required_audience, $json_body));
        }

        // All good.
        return new Google_Auth_LoginTicket($envelope, $payload);
    }

    /**
     * Add a parameter to the auth params if not empty string.
     */
    private function maybeAddParam($params, $name) {
        $param = $this->client->getClassConfig($this, $name);
        if ($param != '') {
            $params[$name] = $param;
        }

        return $params;
    }
}
