Proyectos de Subversion Moodle

<?php

// This file is part of BasicLTI4Moodle

//

// BasicLTI4Moodle is an IMS BasicLTI (Basic Learning Tools for Interoperability)

// consumer for Moodle 1.9 and Moodle 2.0. BasicLTI is a IMS Standard that allows web

// based learning tools to be easily integrated in LMS as native ones. The IMS BasicLTI

// specification is part of the IMS standard Common Cartridge 1.1 Sakai and other main LMS

// are already supporting or going to support BasicLTI. This project Implements the consumer

// for Moodle. Moodle is a Free Open source Learning Management System by Martin Dougiamas.

// BasicLTI4Moodle is a project iniciated and leaded by Ludo(Marc Alier) and Jordi Piguillem

// at the GESSI research group at UPC.

// SimpleLTI consumer for Moodle is an implementation of the early specification of LTI

// by Charles Severance (Dr Chuck) htp://dr-chuck.com , developed by Jordi Piguillem in a

// Google Summer of Code 2008 project co-mentored by Charles Severance and Marc Alier.

//

// BasicLTI4Moodle is copyright 2009 by Marc Alier Forment, Jordi Piguillem and Nikolas Galanis

// of the Universitat Politecnica de Catalunya http://www.upc.edu

// Contact info: Marc Alier Forment granludo @ gmail.com or marc.alier @ upc.edu

//

// OAuth.php is distributed under the MIT License

//

// The MIT License

//

// Copyright (c) 2007 Andy Smith

//

// Permission is hereby granted, free of charge, to any person obtaining a copy

// of this software and associated documentation files (the "Software"), to deal

// in the Software without restriction, including without limitation the rights

// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

// copies of the Software, and to permit persons to whom the Software is

// furnished to do so, subject to the following conditions:

//

// The above copyright notice and this permission notice shall be included in

// all copies or substantial portions of the Software.

//

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

// THE SOFTWARE.

//

// 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/>.

/**

 * This file contains the OAuth 1.0a implementation used for support for LTI 1.1.

 *

 * @package    mod_lti

 * @copyright moodle

 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later

 */

namespace moodle\mod\lti;//Using a namespace as the basicLTI module imports classes with the same names

defined('MOODLE_INTERNAL') || die;

$lastcomputedsignature = false;

/**

 * Generic exception class

 */

class OAuthException extends \Exception {

    // pass

}

/**

 * OAuth 1.0 Consumer class

 */

class OAuthConsumer {

    public $key;

    public $secret;

    /** @var string|null callback URL. */

    public ?string $callback_url;

    function __construct($key, $secret, $callback_url = null) {

        $this->key = $key;

        $this->secret = $secret;

        $this->callback_url = $callback_url;

    }

    function __toString() {

        return "OAuthConsumer[key=$this->key,secret=$this->secret]";

    }

}

class OAuthToken {

    // access tokens and request tokens

    public $key;

    public $secret;

    /**

     * key = the token

     * secret = the token secret

     */

    function __construct($key, $secret) {

        $this->key = $key;

        $this->secret = $secret;

    }

    /**

     * generates the basic string serialization of a token that a server

     * would respond to request_token and access_token calls with

     */

    function to_string() {

        return "oauth_token=" .

        OAuthUtil::urlencode_rfc3986($this->key) .

        "&oauth_token_secret=" .

        OAuthUtil::urlencode_rfc3986($this->secret);

    }

    function __toString() {

        return $this->to_string();

    }

}

class OAuthSignatureMethod {

    public function check_signature(&$request, $consumer, $token, $signature) {

        $built = $this->build_signature($request, $consumer, $token);

        return $built == $signature;

    }

}

/**

 * Base class for the HMac based signature methods.

 */

abstract class OAuthSignatureMethod_HMAC extends OAuthSignatureMethod {

    /**

     * Name of the Algorithm used.

     *

     * @return string algorithm name.

     */

    abstract public function get_name(): string;

    public function build_signature($request, $consumer, $token) {

        global $lastcomputedsignature;

        $lastcomputedsignature = false;

        $basestring = $request->get_signature_base_string();

        $request->base_string = $basestring;

        $key_parts = array(

            $consumer->secret,

             ($token) ? $token->secret : ""

        );

        $key_parts = OAuthUtil::urlencode_rfc3986($key_parts);

        $key = implode('&', $key_parts);

        $computedsignature = base64_encode(hash_hmac(strtolower(substr($this->get_name(), 5)), $basestring, $key, true));

        $lastcomputedsignature = $computedsignature;

        return $computedsignature;

    }

}

/**

 * Implementation for SHA 1.

 */

class OAuthSignatureMethod_HMAC_SHA1 extends OAuthSignatureMethod_HMAC {

    /**

     * Name of the Algorithm used.

     *

     * @return string algorithm name.

     */

    public function get_name(): string {

        return "HMAC-SHA1";

    }

}

/**

 * Implementation for SHA 256.

 */

class OAuthSignatureMethod_HMAC_SHA256 extends OAuthSignatureMethod_HMAC {

    /**

     * Name of the Algorithm used.

     *

     * @return string algorithm name.

     */

    public function get_name(): string {

        return "HMAC-SHA256";

    }

}

class OAuthSignatureMethod_PLAINTEXT extends OAuthSignatureMethod {

    /**

     * Name of the Algorithm used.

     *

     * @return string algorithm name.

     */

    public function get_name(): string {

        return "PLAINTEXT";

    }

    public function build_signature($request, $consumer, $token) {

        $sig = array(

            OAuthUtil::urlencode_rfc3986($consumer->secret)

        );

        if ($token) {

            array_push($sig, OAuthUtil::urlencode_rfc3986($token->secret));

        } else {

            array_push($sig, '');

        }

        $raw = implode("&", $sig);

        // for debug purposes

        $request->base_string = $raw;

        return OAuthUtil::urlencode_rfc3986($raw);

    }

}

class OAuthSignatureMethod_RSA_SHA1 extends OAuthSignatureMethod {

    /**

     * Name of the Algorithm used.

     *

     * @return string algorithm name.

     */

    public function get_name(): string {

        return "RSA-SHA1";

    }

    protected function fetch_public_cert(&$request) {

        // not implemented yet, ideas are:

        // (1) do a lookup in a table of trusted certs keyed off of consumer

        // (2) fetch via http using a url provided by the requester

        // (3) some sort of specific discovery code based on request

        //

        // either way should return a string representation of the certificate

        throw new OAuthException("fetch_public_cert not implemented");

    }

    protected function fetch_private_cert(&$request) {

        // not implemented yet, ideas are:

        // (1) do a lookup in a table of trusted certs keyed off of consumer

        //

        // either way should return a string representation of the certificate

        throw new OAuthException("fetch_private_cert not implemented");

    }

    public function build_signature(&$request, $consumer, $token) {

        $base_string = $request->get_signature_base_string();

        $request->base_string = $base_string;

        // Fetch the private key cert based on the request

        $cert = $this->fetch_private_cert($request);

        // Pull the private key ID from the certificate

        $privatekeyid = openssl_get_privatekey($cert);

        // Sign using the key

        $ok = openssl_sign($base_string, $signature, $privatekeyid);

        // Avoid passing null values to base64_encode.

        if (!$ok) {

            throw new OAuthException("OpenSSL unable to sign data");

        }

        return base64_encode($signature);

    }

    public function check_signature(&$request, $consumer, $token, $signature) {

        $decoded_sig = base64_decode($signature);

        $base_string = $request->get_signature_base_string();

        // Fetch the public key cert based on the request

        $cert = $this->fetch_public_cert($request);

        // Pull the public key ID from the certificate

        $publickeyid = openssl_get_publickey($cert);

        // Check the computed signature against the one passed in the query

        $ok = openssl_verify($base_string, $decoded_sig, $publickeyid);

        return $ok == 1;

    }

}

class OAuthRequest {

    private $parameters;

    private $http_method;

    private $http_url;

    // for debug purposes

    public $base_string;

    public static $version = '1.0';

    public static $POST_INPUT = 'php://input';

    function __construct($http_method, $http_url, $parameters = null) {

        @$parameters or $parameters = array();

        $this->parameters = $parameters;

        $this->http_method = $http_method;

        $this->http_url = $http_url;

    }

    /**

     * attempt to build up a request from what was passed to the server

     */

    public static function from_request($http_method = null, $http_url = null, $parameters = null) {

        $scheme = (!is_https()) ? 'http' : 'https';

        $port = "";

        if ($_SERVER['SERVER_PORT'] != "80" && $_SERVER['SERVER_PORT'] != "443" && strpos(':', $_SERVER['HTTP_HOST']) < 0) {

            $port = ':' . $_SERVER['SERVER_PORT'];

        }

        @$http_url or $http_url = $scheme .

        '://' . $_SERVER['HTTP_HOST'] .

        $port .

        $_SERVER['REQUEST_URI'];

        @$http_method or $http_method = $_SERVER['REQUEST_METHOD'];

        // We weren't handed any parameters, so let's find the ones relevant to

        // this request.

        // If you run XML-RPC or similar you should use this to provide your own

        // parsed parameter-list

        if (!$parameters) {

            // Find request headers

            $request_headers = OAuthUtil::get_headers();

            // Parse the query-string to find GET parameters

            $parameters = OAuthUtil::parse_parameters($_SERVER['QUERY_STRING']);

            $ourpost = $_POST;

            // Add POST Parameters if they exist

            $parameters = array_merge($parameters, $ourpost);

            // We have a Authorization-header with OAuth data. Parse the header

            // and add those overriding any duplicates from GET or POST

            if (@substr($request_headers['Authorization'], 0, 6) == "OAuth ") {

                $header_parameters = OAuthUtil::split_header($request_headers['Authorization']);

                $parameters = array_merge($parameters, $header_parameters);

            }

        }

        return new OAuthRequest($http_method, $http_url, $parameters);

    }

    /**

     * pretty much a helper function to set up the request

     */

    public static function from_consumer_and_token($consumer, $token, $http_method, $http_url, $parameters = null) {

        @$parameters or $parameters = array();

        $defaults = array(

            "oauth_version" => self::$version,

            "oauth_nonce" => self::generate_nonce(),

            "oauth_timestamp" => self::generate_timestamp(),

            "oauth_consumer_key" => $consumer->key

        );

        if ($token) {

            $defaults['oauth_token'] = $token->key;

        }

        $parameters = array_merge($defaults, $parameters);

        // Parse the query-string to find and add GET parameters

        $parts = parse_url($http_url);

        if (isset($parts['query'])) {

            $qparms = OAuthUtil::parse_parameters($parts['query']);

            $parameters = array_merge($qparms, $parameters);

        }

        return new OAuthRequest($http_method, $http_url, $parameters);

    }

    public function set_parameter($name, $value, $allow_duplicates = true) {

        if ($allow_duplicates && isset($this->parameters[$name])) {

            // We have already added parameter(s) with this name, so add to the list

            if (is_scalar($this->parameters[$name])) {

                // This is the first duplicate, so transform scalar (string)

                // into an array so we can add the duplicates

                $this->parameters[$name] = array($this->parameters[$name]);

            }

            $this->parameters[$name][] = $value;

        } else {

            $this->parameters[$name] = $value;

        }

    }

    public function get_parameter($name) {

        return isset($this->parameters[$name]) ? $this->parameters[$name] : null;

    }

    public function get_parameters() {

        return $this->parameters;

    }

    public function unset_parameter($name) {

        unset($this->parameters[$name]);

    }

    /**

     * The request parameters, sorted and concatenated into a normalized string.

     * @return string

     */

    public function get_signable_parameters() {

        // Grab all parameters

        $params = $this->parameters;

        // Remove oauth_signature if present

        // Ref: Spec: 9.1.1 ("The oauth_signature parameter MUST be excluded.")

        if (isset($params['oauth_signature'])) {

            unset($params['oauth_signature']);

        }

        return OAuthUtil::build_http_query($params);

    }

    /**

     * Returns the base string of this request

     *

     * The base string defined as the method, the url

     * and the parameters (normalized), each urlencoded

     * and the concated with &.

     */

    public function get_signature_base_string() {

        $parts = array(

            $this->get_normalized_http_method(),

            $this->get_normalized_http_url(),

            $this->get_signable_parameters()

        );

        $parts = OAuthUtil::urlencode_rfc3986($parts);

        return implode('&', $parts);

    }

    /**

     * just uppercases the http method

     */

    public function get_normalized_http_method() {

        return strtoupper($this->http_method);

    }

    /**

     * Parses {@see http_url} and returns normalized scheme://host/path if non-empty, otherwise return empty string

     *

     * @return string

     */

    public function get_normalized_http_url() {

        if ($this->http_url === '') {

            return '';

        }

        $parts = parse_url($this->http_url);

        $port = @$parts['port'];

        $scheme = $parts['scheme'];

        $host = $parts['host'];

        $path = @$parts['path'];

        $port or $port = ($scheme == 'https') ? '443' : '80';

        if (($scheme == 'https' && $port != '443') || ($scheme == 'http' && $port != '80')) {

            $host = "$host:$port";

        }

        return "$scheme://$host$path";

    }

    /**

     * builds a url usable for a GET request

     */

    public function to_url() {

        $post_data = $this->to_postdata();

        $out = $this->get_normalized_http_url();

        if ($post_data) {

            $out .= '?'.$post_data;

        }

        return $out;

    }

    /**

     * builds the data one would send in a POST request

     */

    public function to_postdata() {

        return OAuthUtil::build_http_query($this->parameters);

    }

    /**

     * builds the Authorization: header

     */

    public function to_header() {

        $out = 'Authorization: OAuth realm=""';

        $total = array();

        foreach ($this->parameters as $k => $v) {

            if (substr($k, 0, 5) != "oauth") {

                continue;

            }

            if (is_array($v)) {

                throw new OAuthException('Arrays not supported in headers');

            }

            $out .= ',' .

            OAuthUtil::urlencode_rfc3986($k) .

            '="' .

            OAuthUtil::urlencode_rfc3986($v) .

            '"';

        }

        return $out;

    }

    public function __toString() {

        return $this->to_url();

    }

    public function sign_request($signature_method, $consumer, $token) {

        $this->set_parameter("oauth_signature_method", $signature_method->get_name(), false);

        $signature = $this->build_signature($signature_method, $consumer, $token);

        $this->set_parameter("oauth_signature", $signature, false);

    }

    public function build_signature($signature_method, $consumer, $token) {

        $signature = $signature_method->build_signature($this, $consumer, $token);

        return $signature;

    }

    /**

     * util function: current timestamp

     */

    private static function generate_timestamp() {

        return time();

    }

    /**

     * util function: current nonce

     */

    private static function generate_nonce() {

        $mt = microtime();

        $rand = mt_rand();

        return md5($mt.$rand); // md5s look nicer than numbers

    }

}

class OAuthServer {

    protected $timestamp_threshold = 300; // in seconds, five minutes

    protected $version = 1.0; // hi blaine

    protected $signature_methods = array();

    protected $data_store;

    function __construct($data_store) {

        $this->data_store = $data_store;

    }

    public function add_signature_method($signature_method) {

        $this->signature_methods[$signature_method->get_name()] = $signature_method;

    }

    // high level functions

    /**

     * process a request_token request

     * returns the request token on success

     */

    public function fetch_request_token(&$request) {

        $this->get_version($request);

        $consumer = $this->get_consumer($request);

        // no token required for the initial token request

        $token = null;

        $this->check_signature($request, $consumer, $token);

        $new_token = $this->data_store->new_request_token($consumer);

        return $new_token;

    }

    /**

     * process an access_token request

     * returns the access token on success

     */

    public function fetch_access_token(&$request) {

        $this->get_version($request);

        $consumer = $this->get_consumer($request);

        // requires authorized request token

        $token = $this->get_token($request, $consumer, "request");

        $this->check_signature($request, $consumer, $token);

        $new_token = $this->data_store->new_access_token($token, $consumer);

        return $new_token;

    }

    /**

     * verify an api call, checks all the parameters

     */

    public function verify_request(&$request) {

        global $lastcomputedsignature;

        $lastcomputedsignature = false;

        $this->get_version($request);

        $consumer = $this->get_consumer($request);

        $token = $this->get_token($request, $consumer, "access");

        $this->check_signature($request, $consumer, $token);

        return array(

            $consumer,

            $token

        );

    }

    // Internals from here

    /**

     * version 1

     */

    private function get_version(&$request) {

        $version = $request->get_parameter("oauth_version");

        if (!$version) {

            $version = 1.0;

        }

        if ($version && $version != $this->version) {

            throw new OAuthException("OAuth version '$version' not supported");

        }

        return $version;

    }

    /**

     * figure out the signature with some defaults

     */

    private function get_signature_method(&$request) {

        $signature_method = @ $request->get_parameter("oauth_signature_method");

        if (!$signature_method) {

            $signature_method = "PLAINTEXT";

        }

        if (!in_array($signature_method, array_keys($this->signature_methods))) {

            throw new OAuthException("Signature method '$signature_method' not supported " .

            "try one of the following: " .

            implode(", ", array_keys($this->signature_methods)));

        }

        return $this->signature_methods[$signature_method];

    }

    /**

     * try to find the consumer for the provided request's consumer key

     */

    private function get_consumer(&$request) {

        $consumer_key = @ $request->get_parameter("oauth_consumer_key");

        if (!$consumer_key) {

            throw new OAuthException("Invalid consumer key");

        }

        $consumer = $this->data_store->lookup_consumer($consumer_key);

        if (!$consumer) {

            throw new OAuthException("Invalid consumer");

        }

        return $consumer;

    }

    /**

     * try to find the token for the provided request's token key

     */

    private function get_token(&$request, $consumer, $token_type = "access") {

        $token_field = @ $request->get_parameter('oauth_token');

        if (!$token_field) {

            return false;

        }

        $token = $this->data_store->lookup_token($consumer, $token_type, $token_field);

        if (!$token) {

            throw new OAuthException("Invalid $token_type token: $token_field");

        }

        return $token;

    }

    /**

     * all-in-one function to check the signature on a request

     * should guess the signature method appropriately

     */

    private function check_signature(&$request, $consumer, $token) {

        // this should probably be in a different method

        global $lastcomputedsignature;

        $lastcomputedsignature = false;

        $timestamp = @ $request->get_parameter('oauth_timestamp');

        $nonce = @ $request->get_parameter('oauth_nonce');

        $this->check_timestamp($timestamp);

        $this->check_nonce($consumer, $token, $nonce, $timestamp);

        $signature_method = $this->get_signature_method($request);

        $signature = $request->get_parameter('oauth_signature');

        $valid_sig = $signature_method->check_signature($request, $consumer, $token, $signature);

        if (!$valid_sig) {

            $ex_text = "Invalid signature";

            if ($lastcomputedsignature) {

                $ex_text = $ex_text . " ours= $lastcomputedsignature yours=$signature";

            }

            throw new OAuthException($ex_text);

        }

    }

    /**

     * check that the timestamp is new enough

     */

    private function check_timestamp($timestamp) {

        // verify that timestamp is recentish

        $now = time();

        if ($now - $timestamp > $this->timestamp_threshold) {

            throw new OAuthException("Expired timestamp, yours $timestamp, ours $now");

        }

    }

    /**

     * check that the nonce is not repeated

     */

    private function check_nonce($consumer, $token, $nonce, $timestamp) {

        // verify that the nonce is uniqueish

        $found = $this->data_store->lookup_nonce($consumer, $token, $nonce, $timestamp);

        if ($found) {

            throw new OAuthException("Nonce already used: $nonce");

        }

    }

}

class OAuthDataStore {

    function lookup_consumer($consumer_key) {

        // implement me

    }

    function lookup_token($consumer, $token_type, $token) {

        // implement me

    }

    function lookup_nonce($consumer, $token, $nonce, $timestamp) {

        // implement me

    }

    function new_request_token($consumer) {

        // return a new token attached to this consumer

    }

    function new_access_token($token, $consumer) {

        // return a new access token attached to this consumer

        // for the user associated with this token if the request token

        // is authorized

        // should also invalidate the request token

    }

}

class OAuthUtil {

    public static function urlencode_rfc3986($input) {

        if (is_array($input)) {

            return array_map(array(

                'moodle\mod\lti\OAuthUtil',

                'urlencode_rfc3986'

            ), $input);

        } else {

            if (is_scalar($input)) {

                return str_replace('+', ' ', str_replace('%7E', '~', rawurlencode($input)));

            } else {

                return '';

            }

        }

    }

    // This decode function isn't taking into consideration the above

    // modifications to the encoding process. However, this method doesn't

    // seem to be used anywhere so leaving it as is.

    public static function urldecode_rfc3986($string) {

        return urldecode($string);

    }

    // Utility function for turning the Authorization: header into

    // parameters, has to do some unescaping

    // Can filter out any non-oauth parameters if needed (default behaviour)

    public static function split_header($header, $only_allow_oauth_parameters = true) {

        $pattern = '/(([-_a-z]*)=("([^"]*)"|([^,]*)),?)/';

        $offset = 0;

        $params = array();

        while (preg_match($pattern, $header, $matches, PREG_OFFSET_CAPTURE, $offset) > 0) {

            $match = $matches[0];

            $header_name = $matches[2][0];

            $header_content = (isset($matches[5])) ? $matches[5][0] : $matches[4][0];

            if (preg_match('/^oauth_/', $header_name) || !$only_allow_oauth_parameters) {

                $params[$header_name] = self::urldecode_rfc3986($header_content);

            }

            $offset = $match[1] + strlen($match[0]);

        }

        if (isset($params['realm'])) {

            unset($params['realm']);

        }

        return $params;

    }

    // helper to try to sort out headers for people who aren't running apache

    public static function get_headers() {

        if (function_exists('apache_request_headers')) {

            // we need this to get the actual Authorization: header

            // because apache tends to tell us it doesn't exist

            $in = apache_request_headers();

            $out = array();

            foreach ($in as $key => $value) {

                $key = str_replace(" ", "-", ucwords(strtolower(str_replace("-", " ", $key))));

                $out[$key] = $value;

            }

            return $out;

        }

        // otherwise we don't have apache and are just going to have to hope

        // that $_SERVER actually contains what we need

        $out = array();

        foreach ($_SERVER as $key => $value) {

            if (substr($key, 0, 5) == "HTTP_") {

                // this is chaos, basically it is just there to capitalize the first

                // letter of every word that is not an initial HTTP and strip HTTP

                // code from przemek

                $key = str_replace(" ", "-", ucwords(strtolower(str_replace("_", " ", substr($key, 5)))));

                $out[$key] = $value;

            }

        }

        return $out;

    }

    // This function takes a input like a=b&a=c&d=e and returns the parsed

    // parameters like this

    // array('a' => array('b','c'), 'd' => 'e')

    public static function parse_parameters($input) {

        if (!isset($input) || !$input) {

            return array();

        }

        $pairs = explode('&', $input);

        $parsed_parameters = array();

        foreach ($pairs as $pair) {

            $split = explode('=', $pair, 2);

            $parameter = self::urldecode_rfc3986($split[0]);

            $value = isset($split[1]) ? self::urldecode_rfc3986($split[1]) : '';

            if (isset($parsed_parameters[$parameter])) {

                // We have already recieved parameter(s) with this name, so add to the list

                // of parameters with this name

                if (is_scalar($parsed_parameters[$parameter])) {

                    // This is the first duplicate, so transform scalar (string) into an array

                    // so we can add the duplicates

                    $parsed_parameters[$parameter] = array(

                        $parsed_parameters[$parameter]

                    );

                }

                $parsed_parameters[$parameter][] = $value;

            } else {

                $parsed_parameters[$parameter] = $value;

            }

        }

        return $parsed_parameters;

    }

    public static function build_http_query($params) {

        if (!$params) {

            return '';

        }

        // Urlencode both keys and values

        $keys = self::urlencode_rfc3986(array_keys($params));

        $values = self::urlencode_rfc3986(array_values($params));

        $params = array_combine($keys, $values);

        // Parameters are sorted by name, using lexicographical byte value ordering.

        // Ref: Spec: 9.1.1 (1)

        uksort($params, 'strcmp');

        $pairs = array();

        foreach ($params as $parameter => $value) {

            if (is_array($value)) {

                // If two or more parameters share the same name, they are sorted by their value

                // Ref: Spec: 9.1.1 (1)

                natsort($value);

                foreach ($value as $duplicate_value) {

                    $pairs[] = $parameter . '=' . $duplicate_value;

                }

            } else {

                $pairs[] = $parameter . '=' . $value;

            }

        }

        // For each parameter, the name is separated from the corresponding value by an '=' character (ASCII code 61)

        // Each name-value pair is separated by an '&' character (ASCII code 38)

        return implode('&', $pairs);

    }

}