<?php

// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**
 * An oauth2 redirection endpoint which can be used for an application:
 * http://tools.ietf.org/html/draft-ietf-oauth-v2-26#section-3.1.2
 *
 * This is used because some oauth servers will not allow a redirect urls
 * with get params (like repository callback) and that needs to be called
 * using the state param.
 *
 * @package    core
 * @copyright  2012 Dan Poltawski
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

require_once(__DIR__ . '/../config.php');

// The state parameter we've given (used in moodle as a redirect url).
// Per https://www.rfc-editor.org/rfc/rfc6749#section-4.1.2.1, state is required, even during error responses.
$state = required_param('state', PARAM_LOCALURL);
$redirecturl = new moodle_url($state);
$params = $redirecturl->params();

$error = optional_param('error', '', PARAM_RAW);

if ($error) {
    $message = optional_param('error_description', null, PARAM_RAW);

    // Errors can occur for authenticated users, such as when a user denies authorization for some internal service call.
    // In such cases, propagate the error to the component redirect URI.
    if (isloggedin()) {
        if (isset($params['sesskey']) && confirm_sesskey($params['sesskey'])) {
            $redirecturl->param('error', $error);
            if ($message) {
                $redirecturl->param('error_description', $message);
            }
            redirect($redirecturl);
        }
    }

    // Not logged in or the sesskey verification failed, redirect to login + show errors.
    $SESSION->loginerrormsg = $message ?? $error;
    redirect(new moodle_url(get_login_url()));
}

// The authorization code generated by the authorization server.
$code = required_param('code', PARAM_RAW);

if (isset($params['sesskey']) and confirm_sesskey($params['sesskey'])) {
    $redirecturl->param('oauth2code', $code);
    redirect($redirecturl);
} else {
    $SESSION->loginerrormsg = get_string('invalidsesskey', 'error');
    redirect(new moodle_url(get_login_url()));
}