<?php

// http://oauth.googlecode.com/svn/code/php/OAuth.php

// rev 1276,	July 4, 2014



// vim: foldmethod=marker



/* Generic exception class

 */

if (!class_exists('OAuthException')) {

  class OAuthException extends Exception {

    // pass

  }

}



class OAuthConsumer {

  public $key;

  public $secret;



  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();

  }

}



/**

 * A class for implementing a Signature Method

 * See section 9 ("Signing Requests") in the spec

 */

abstract class OAuthSignatureMethod {

  /**

   * Needs to return the name of the Signature Method (ie HMAC-SHA1)

   * @return string

   */

  abstract public function get_name();



  /**

   * Build up the signature

   * NOTE: The output of this function MUST NOT be urlencoded.

   * the encoding is handled in OAuthRequest when the final

   * request is serialized

   * @param OAuthRequest $request

   * @param OAuthConsumer $consumer

   * @param OAuthToken $token

   * @return string

   */

  abstract public function build_signature($request, $consumer, $token);



  /**

   * Verifies that a given signature is correct

   * @param OAuthRequest $request

   * @param OAuthConsumer $consumer

   * @param OAuthToken $token

   * @param string $signature

   * @return bool

   */

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

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



    // Check for zero length, although unlikely here

    if (strlen($built) == 0 || strlen($signature) == 0) {

      return false;

    }



    if (strlen($built) != strlen($signature)) {

      return false;

    }



    // Avoid a timing leak with a (hopefully) time insensitive compare

    $result = 0;

    for ($i = 0; $i < strlen($signature); $i++) {

      $result |= ord($built{$i}) ^ ord($signature{$i});

    }



    return $result == 0;

  }

}



/**

 * The HMAC-SHA1 signature method uses the HMAC-SHA1 signature algorithm as defined in [RFC2104] 

 * where the Signature Base String is the text and the key is the concatenated values (each first 

 * encoded per Parameter Encoding) of the Consumer Secret and Token Secret, separated by an '&' 

 * character (ASCII code 38) even if empty.

 *   - Chapter 9.2 ("HMAC-SHA1")

 */

class OAuthSignatureMethod_HMAC_SHA1 extends OAuthSignatureMethod {

  function get_name() {

    return "HMAC-SHA1";

  }



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

    $base_string = $request->get_signature_base_string();

    $request->base_string = $base_string;



    $key_parts = array(

      $consumer->secret,

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

    );



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

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



    return base64_encode(hash_hmac('sha1', $base_string, $key, true));

  }

}



/**

 * The PLAINTEXT method does not provide any security protection and SHOULD only be used 

 * over a secure channel such as HTTPS. It does not use the Signature Base String.

 *   - Chapter 9.4 ("PLAINTEXT")

 */

class OAuthSignatureMethod_PLAINTEXT extends OAuthSignatureMethod {

  public function get_name() {

    return "PLAINTEXT";

  }



  /**

   * oauth_signature is set to the concatenated encoded values of the Consumer Secret and 

   * Token Secret, separated by a '&' character (ASCII code 38), even if either secret is 

   * empty. The result MUST be encoded again.

   *   - Chapter 9.4.1 ("Generating Signatures")

   *

   * Please note that the second encoding MUST NOT happen in the SignatureMethod, as

   * OAuthRequest handles this!

   */

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

    $key_parts = array(

      $consumer->secret,

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

    );



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

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

    $request->base_string = $key;



    return $key;

  }

}



/**

 * The RSA-SHA1 signature method uses the RSASSA-PKCS1-v1_5 signature algorithm as defined in 

 * [RFC3447] section 8.2 (more simply known as PKCS#1), using SHA-1 as the hash function for 

 * EMSA-PKCS1-v1_5. It is assumed that the Consumer has provided its RSA public key in a 

 * verified way to the Service Provider, in a manner which is beyond the scope of this 

 * specification.

 *   - Chapter 9.3 ("RSA-SHA1")

 */

abstract class OAuthSignatureMethod_RSA_SHA1 extends OAuthSignatureMethod {

  public function get_name() {

    return "RSA-SHA1";

  }



  // Up to the SP to implement this lookup of keys. Possible 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

  protected abstract function fetch_public_cert(&$request);



  // Up to the SP to implement this lookup of keys. Possible 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

  protected abstract function fetch_private_cert(&$request);



  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);



    // Release the key resource

    openssl_free_key($privatekeyid);



    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);



    // Release the key resource

    openssl_free_key($publickeyid);



    return $ok == 1;

  }

}



class OAuthRequest {

  protected $parameters;

  protected $http_method;

  protected $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) {

    $parameters = ($parameters) ? $parameters : array();

    $parameters = array_merge( OAuthUtil::parse_parameters(parse_url($http_url, PHP_URL_QUERY)), $parameters);

    $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) {

    $scheme = (!isset($_SERVER['HTTPS']) || $_SERVER['HTTPS'] != "on")

              ? 'http'

              : 'https';

    if (isset($_SERVER['HTTP_X_FORWARDED_PROTO'])) {

      $scheme = $_SERVER['HTTP_X_FORWARDED_PROTO'];

    }

    $http_url = ($http_url) ? $http_url : $scheme .

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

                              ':' .

                              $_SERVER['SERVER_PORT'] .

                              $_SERVER['REQUEST_URI'];

    $http_method = ($http_method) ? $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']);



      // It's a POST request of the proper content-type, so parse POST

      // parameters and add those overriding any duplicates from GET

      if ($http_method == "POST"

          &&  isset($request_headers['Content-Type'])

          && strstr($request_headers['Content-Type'],

                     'application/x-www-form-urlencoded')

          ) {

        $post_data = OAuthUtil::parse_parameters(

          file_get_contents(self::$POST_INPUT)

        );

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

      }



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

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

      if (isset($request_headers['Authorization']) && substr($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) {

    $parameters = ($parameters) ?  $parameters : array();

    $defaults = array("oauth_version" => OAuthRequest::$version,

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

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

                      "oauth_consumer_key" => $consumer->key);

    if ($token)

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



    $parameters = array_merge($defaults, $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 the url and rebuilds it to be

   * scheme://host/path

   */

  public function get_normalized_http_url() {

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



    $scheme = (isset($parts['scheme'])) ? $parts['scheme'] : 'http';

    $port = (isset($parts['port'])) ? $parts['port'] : (($scheme == 'https') ? '443' : '80');

    $host = (isset($parts['host'])) ? strtolower($parts['host']) : '';

    $path = (isset($parts['path'])) ? $parts['path'] : '';



    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($realm=null) {

    $first = true;

	if($realm) {

      $out = 'Authorization: OAuth realm="' . OAuthUtil::urlencode_rfc3986($realm) . '"';

      $first = false;

    } else

      $out = 'Authorization: OAuth';



    $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');

      }

      $out .= ($first) ? ' ' : ',';

      $out .= OAuthUtil::urlencode_rfc3986($k) .

              '="' .

              OAuthUtil::urlencode_rfc3986($v) .

              '"';

      $first = false;

    }

    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);



    // Rev A change

    $callback = $request->get_parameter('oauth_callback');

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



    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);



    // Rev A change

    $verifier = $request->get_parameter('oauth_verifier');

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



    return $new_token;

  }



  /**

   * verify an api call, checks all the parameters

   */

  public function verify_request(&$request) {

    $this->get_version($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) {

      // Service Providers MUST assume the protocol version to be 1.0 if this parameter is not present. 

      // Chapter 7.0 ("Accessing Protected Ressources")

      $version = '1.0';

    }

    if ($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 instanceof OAuthRequest 

        ? $request->get_parameter("oauth_signature_method")

        : NULL;



    if (!$signature_method) {

      // According to chapter 7 ("Accessing Protected Ressources") the signature-method

      // parameter is required, and we can't just fallback to PLAINTEXT

      throw new OAuthException('No signature method parameter. This parameter is required');

    }



    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 instanceof OAuthRequest 

        ? $request->get_parameter("oauth_consumer_key")

        : NULL;



    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 instanceof OAuthRequest

         ? $request->get_parameter('oauth_token')

         : NULL;



    $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

    $timestamp = $request instanceof OAuthRequest

        ? $request->get_parameter('oauth_timestamp')

        : NULL;

    $nonce = $request instanceof OAuthRequest

        ? $request->get_parameter('oauth_nonce')

        : NULL;



    $this->check_timestamp($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) {

      throw new OAuthException("Invalid signature");

    }

  }



  /**

   * check that the timestamp is new enough

   */

  private function check_timestamp($timestamp) {

    if( ! $timestamp )

      throw new OAuthException(

        'Missing timestamp parameter. The parameter is required'

      );

    

    // verify that timestamp is recentish

    $now = time();

    if (abs($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) {

    if( ! $nonce )

      throw new OAuthException(

        'Missing nonce parameter. The parameter is required'

      );



    // 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, $callback = null) {

    // return a new token attached to this consumer

  }



  function new_access_token($token, $consumer, $verifier = null) {

    // 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('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)

  // May 28th, 2010 - method updated to tjerk.meesters for a speed improvement.

  //                  see http://code.google.com/p/oauth/issues/detail?id=163

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

    $params = array();

    if (preg_match_all('/('.($only_allow_oauth_parameters ? 'oauth_' : '').'[a-z_-]*)=(:?"([^"]*)"|([^,]*))/', $header, $matches)) {

      foreach ($matches[1] as $i => $h) {

        $params[$h] = OAuthUtil::urldecode_rfc3986(empty($matches[3][$i]) ? $matches[4][$i] : $matches[3][$i]);

      }

      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

      $headers = apache_request_headers();



      // sanitize the output of apache_request_headers because

      // we always want the keys to be Cased-Like-This and arh()

      // returns the headers in the same case as they are in the

      // request

      $out = array();

      foreach ($headers AS $key => $value) {

        $key = str_replace(

            " ",

            "-",

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

          );

        $out[$key] = $value;

      }

    } else {

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

      // that $_SERVER actually contains what we need

      $out = array();

      if( isset($_SERVER['CONTENT_TYPE']) )

        $out['Content-Type'] = $_SERVER['CONTENT_TYPE'];

      if( isset($_ENV['CONTENT_TYPE']) )

        $out['Content-Type'] = $_ENV['CONTENT_TYPE'];



      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);

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

      $value = isset($split[1]) ? OAuthUtil::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

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

    $values = OAuthUtil::urlencode_rfc3986(array_values($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)

        // June 12th, 2010 - changed to sort because of issue 164 by hidetaka

        sort($value, SORT_STRING);

        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);

  }

}

