enrol/lti/ims-blti/OAuth.php

   1 <?php
   2 // vim: foldmethod=marker
   3
   4 $OAuth_last_computed_siguature = false;
   5
   6 /* Generic exception class
   7  */
   8 class OAuthException extends \Exception {
   9   // pass
  10 }
  11
  12 class OAuthConsumer {
  13   public $key;
  14   public $secret;
  15
  16   function __construct($key, $secret, $callback_url=NULL) {
  17     $this->key = $key;
  18     $this->secret = $secret;
  19     $this->callback_url = $callback_url;
  20   }
  21
  22   function __toString() {
  23     return "OAuthConsumer[key=$this->key,secret=$this->secret]";
  24   }
  25 }
  26
  27 class OAuthToken {
  28   // access tokens and request tokens
  29   public $key;
  30   public $secret;
  31
  32   /**
  33    * key = the token
  34    * secret = the token secret
  35    */
  36   function __construct($key, $secret) {
  37     $this->key = $key;
  38     $this->secret = $secret;
  39   }
  40
  41   /**
  42    * generates the basic string serialization of a token that a server
  43    * would respond to request_token and access_token calls with
  44    */
  45   function to_string() {
  46     return "oauth_token=" .
  47            OAuthUtil::urlencode_rfc3986($this->key) .
  48            "&oauth_token_secret=" .
  49            OAuthUtil::urlencode_rfc3986($this->secret);
  50   }
  51
  52   function __toString() {
  53     return $this->to_string();
  54   }
  55 }
  56
  57 class OAuthSignatureMethod {
  58   public function check_signature(&$request, $consumer, $token, $signature) {
  59     $built = $this->build_signature($request, $consumer, $token);
  60     return $built == $signature;
  61   }
  62 }
  63
  64 class OAuthSignatureMethod_HMAC_SHA1 extends OAuthSignatureMethod {
  65   function get_name() {
  66     return "HMAC-SHA1";
  67   }
  68
  69   public function build_signature($request, $consumer, $token) {
  70     global $OAuth_last_computed_signature;
  71     $OAuth_last_computed_signature = false;
  72
  73     $base_string = $request->get_signature_base_string();
  74     $request->base_string = $base_string;
  75
  76     $key_parts = array(
  77       $consumer->secret,
  78       ($token) ? $token->secret : ""
  79     );
  80
  81     $key_parts = OAuthUtil::urlencode_rfc3986($key_parts);
  82     $key = implode('&', $key_parts);
  83
  84     $computed_signature = base64_encode(hash_hmac('sha1', $base_string, $key, true));
  85     $OAuth_last_computed_signature = $computed_signature;
  86     return $computed_signature;
  87   }
  88
  89 }
  90
  91 class OAuthSignatureMethod_PLAINTEXT extends OAuthSignatureMethod {
  92   public function get_name() {
  93     return "PLAINTEXT";
  94   }
  95
  96   public function build_signature($request, $consumer, $token) {
  97     $sig = array(
  98       OAuthUtil::urlencode_rfc3986($consumer->secret)
  99     );
 100
 101     if ($token) {
 102       array_push($sig, OAuthUtil::urlencode_rfc3986($token->secret));
 103     } else {
 104       array_push($sig, '');
 105     }
 106
 107     $raw = implode("&", $sig);
 108     // for debug purposes
 109     $request->base_string = $raw;
 110
 111     return OAuthUtil::urlencode_rfc3986($raw);
 112   }
 113 }
 114
 115 class OAuthSignatureMethod_RSA_SHA1 extends OAuthSignatureMethod {
 116   public function get_name() {
 117     return "RSA-SHA1";
 118   }
 119
 120   protected function fetch_public_cert(&$request) {
 121     // not implemented yet, ideas are:
 122     // (1) do a lookup in a table of trusted certs keyed off of consumer
 123     // (2) fetch via http using a url provided by the requester
 124     // (3) some sort of specific discovery code based on request
 125     //
 126     // either way should return a string representation of the certificate
 127     throw Exception("fetch_public_cert not implemented");
 128   }
 129
 130   protected function fetch_private_cert(&$request) {
 131     // not implemented yet, ideas are:
 132     // (1) do a lookup in a table of trusted certs keyed off of consumer
 133     //
 134     // either way should return a string representation of the certificate
 135     throw Exception("fetch_private_cert not implemented");
 136   }
 137
 138   public function build_signature(&$request, $consumer, $token) {
 139     $base_string = $request->get_signature_base_string();
 140     $request->base_string = $base_string;
 141
 142     // Fetch the private key cert based on the request
 143     $cert = $this->fetch_private_cert($request);
 144
 145     // Pull the private key ID from the certificate
 146     $privatekeyid = openssl_get_privatekey($cert);
 147
 148     // Sign using the key
 149     $ok = openssl_sign($base_string, $signature, $privatekeyid);
 150
 151     // Release the key resource
 152     openssl_free_key($privatekeyid);
 153
 154     return base64_encode($signature);
 155   }
 156
 157   public function check_signature(&$request, $consumer, $token, $signature) {
 158     $decoded_sig = base64_decode($signature);
 159
 160     $base_string = $request->get_signature_base_string();
 161
 162     // Fetch the public key cert based on the request
 163     $cert = $this->fetch_public_cert($request);
 164
 165     // Pull the public key ID from the certificate
 166     $publickeyid = openssl_get_publickey($cert);
 167
 168     // Check the computed signature against the one passed in the query
 169     $ok = openssl_verify($base_string, $decoded_sig, $publickeyid);
 170
 171     // Release the key resource
 172     openssl_free_key($publickeyid);
 173
 174     return $ok == 1;
 175   }
 176 }
 177
 178 class OAuthRequest {
 179   private $parameters;
 180   private $http_method;
 181   private $http_url;
 182   // for debug purposes
 183   public $base_string;
 184   public static $version = '1.0';
 185   public static $POST_INPUT = 'php://input';
 186
 187   function __construct($http_method, $http_url, $parameters=NULL) {
 188     @$parameters or $parameters = array();
 189     $this->parameters = $parameters;
 190     $this->http_method = $http_method;
 191     $this->http_url = $http_url;
 192   }
 193
 194
 195   /**
 196    * attempt to build up a request from what was passed to the server
 197    */
 198   public static function from_request($http_method=NULL, $http_url=NULL, $parameters=NULL) {
 199     $scheme = (!isset($_SERVER['HTTPS']) || $_SERVER['HTTPS'] != "on")
 200               ? 'http'
 201               : 'https';
 202     $port = "";
 203     if ( $_SERVER['SERVER_PORT'] != "80" && $_SERVER['SERVER_PORT'] != "443" &&
 204         strpos(':', $_SERVER['HTTP_HOST']) < 0 ) {
 205       $port =  ':' . $_SERVER['SERVER_PORT'] ;
 206     }
 207     @$http_url or $http_url = $scheme .
 208                               '://' . $_SERVER['HTTP_HOST'] .
 209                               $port .
 210                               $_SERVER['REQUEST_URI'];
 211     @$http_method or $http_method = $_SERVER['REQUEST_METHOD'];
 212
 213     // We weren't handed any parameters, so let's find the ones relevant to
 214     // this request.
 215     // If you run XML-RPC or similar you should use this to provide your own
 216     // parsed parameter-list
 217     if (!$parameters) {
 218       // Find request headers
 219       $request_headers = OAuthUtil::get_headers();
 220
 221       // Parse the query-string to find GET parameters
 222       $parameters = OAuthUtil::parse_parameters($_SERVER['QUERY_STRING']);
 223
 224       $ourpost = $_POST;
 225       // Deal with magic_quotes
 226       // http://www.php.net/manual/en/security.magicquotes.disabling.php
 227       if ( get_magic_quotes_gpc() ) {
 228          $outpost = array();
 229          foreach ($_POST as $k => $v) {
 230             $v = stripslashes($v);
 231             $ourpost[$k] = $v;
 232          }
 233       }
 234      // Add POST Parameters if they exist
 235       $parameters = array_merge($parameters, $ourpost);
 236
 237       // We have a Authorization-header with OAuth data. Parse the header
 238       // and add those overriding any duplicates from GET or POST
 239       if (@substr($request_headers['Authorization'], 0, 6) == "OAuth ") {
 240         $header_parameters = OAuthUtil::split_header(
 241           $request_headers['Authorization']
 242         );
 243         $parameters = array_merge($parameters, $header_parameters);
 244       }
 245
 246     }
 247
 248     return new OAuthRequest($http_method, $http_url, $parameters);
 249   }
 250
 251   /**
 252    * pretty much a helper function to set up the request
 253    */
 254   public static function from_consumer_and_token($consumer, $token, $http_method, $http_url, $parameters=NULL) {
 255     @$parameters or $parameters = array();
 256     $defaults = array("oauth_version" => OAuthRequest::$version,
 257                       "oauth_nonce" => OAuthRequest::generate_nonce(),
 258                       "oauth_timestamp" => OAuthRequest::generate_timestamp(),
 259                       "oauth_consumer_key" => $consumer->key);
 260     if ($token)
 261       $defaults['oauth_token'] = $token->key;
 262
 263     $parameters = array_merge($defaults, $parameters);
 264
 265     // Parse the query-string to find and add GET parameters
 266     $parts = parse_url($http_url);
 267     if ( !empty($parts['query']) ) {
 268       $qparms = OAuthUtil::parse_parameters($parts['query']);
 269       $parameters = array_merge($qparms, $parameters);
 270     }
 271
 272
 273     return new OAuthRequest($http_method, $http_url, $parameters);
 274   }
 275
 276   public function set_parameter($name, $value, $allow_duplicates = true) {
 277     if ($allow_duplicates && isset($this->parameters[$name])) {
 278       // We have already added parameter(s) with this name, so add to the list
 279       if (is_scalar($this->parameters[$name])) {
 280         // This is the first duplicate, so transform scalar (string)
 281         // into an array so we can add the duplicates
 282         $this->parameters[$name] = array($this->parameters[$name]);
 283       }
 284
 285       $this->parameters[$name][] = $value;
 286     } else {
 287       $this->parameters[$name] = $value;
 288     }
 289   }
 290
 291   public function get_parameter($name) {
 292     return isset($this->parameters[$name]) ? $this->parameters[$name] : null;
 293   }
 294
 295   public function get_parameters() {
 296     return $this->parameters;
 297   }
 298
 299   public function unset_parameter($name) {
 300     unset($this->parameters[$name]);
 301   }
 302
 303   /**
 304    * The request parameters, sorted and concatenated into a normalized string.
 305    * @return string
 306    */
 307   public function get_signable_parameters() {
 308     // Grab all parameters
 309     $params = $this->parameters;
 310
 311     // Remove oauth_signature if present
 312     // Ref: Spec: 9.1.1 ("The oauth_signature parameter MUST be excluded.")
 313     if (isset($params['oauth_signature'])) {
 314       unset($params['oauth_signature']);
 315     }
 316
 317     return OAuthUtil::build_http_query($params);
 318   }
 319
 320   /**
 321    * Returns the base string of this request
 322    *
 323    * The base string defined as the method, the url
 324    * and the parameters (normalized), each urlencoded
 325    * and the concated with &.
 326    */
 327   public function get_signature_base_string() {
 328     $parts = array(
 329       $this->get_normalized_http_method(),
 330       $this->get_normalized_http_url(),
 331       $this->get_signable_parameters()
 332     );
 333
 334     $parts = OAuthUtil::urlencode_rfc3986($parts);
 335
 336     return implode('&', $parts);
 337   }
 338
 339   /**
 340    * just uppercases the http method
 341    */
 342   public function get_normalized_http_method() {
 343     return strtoupper($this->http_method);
 344   }
 345
 346   /**
 347    * parses the url and rebuilds it to be
 348    * scheme://host/path
 349    */
 350   public function get_normalized_http_url() {
 351     $parts = parse_url($this->http_url);
 352
 353     $port = @$parts['port'];
 354     $scheme = $parts['scheme'];
 355     $host = $parts['host'];
 356     $path = @$parts['path'];
 357
 358     $port or $port = ($scheme == 'https') ? '443' : '80';
 359
 360     if (($scheme == 'https' && $port != '443')
 361         || ($scheme == 'http' && $port != '80')) {
 362       $host = "$host:$port";
 363     }
 364     return "$scheme://$host$path";
 365   }
 366
 367   /**
 368    * builds a url usable for a GET request
 369    */
 370   public function to_url() {
 371     $post_data = $this->to_postdata();
 372     $out = $this->get_normalized_http_url();
 373     if ($post_data) {
 374       $out .= '?'.$post_data;
 375     }
 376     return $out;
 377   }
 378
 379   /**
 380    * builds the data one would send in a POST request
 381    */
 382   public function to_postdata() {
 383     return OAuthUtil::build_http_query($this->parameters);
 384   }
 385
 386   /**
 387    * builds the Authorization: header
 388    */
 389   public function to_header() {
 390     $out ='Authorization: OAuth realm=""';
 391     $total = array();
 392     foreach ($this->parameters as $k => $v) {
 393       if (substr($k, 0, 5) != "oauth") continue;
 394       if (is_array($v)) {
 395         throw new OAuthException('Arrays not supported in headers');
 396       }
 397       $out .= ',' .
 398               OAuthUtil::urlencode_rfc3986($k) .
 399               '="' .
 400               OAuthUtil::urlencode_rfc3986($v) .
 401               '"';
 402     }
 403     return $out;
 404   }
 405
 406   public function __toString() {
 407     return $this->to_url();
 408   }
 409
 410
 411   public function sign_request($signature_method, $consumer, $token) {
 412     $this->set_parameter(
 413       "oauth_signature_method",
 414       $signature_method->get_name(),
 415       false
 416     );
 417     $signature = $this->build_signature($signature_method, $consumer, $token);
 418     $this->set_parameter("oauth_signature", $signature, false);
 419   }
 420
 421   public function build_signature($signature_method, $consumer, $token) {
 422     $signature = $signature_method->build_signature($this, $consumer, $token);
 423     return $signature;
 424   }
 425
 426   /**
 427    * util function: current timestamp
 428    */
 429   private static function generate_timestamp() {
 430     return time();
 431   }
 432
 433   /**
 434    * util function: current nonce
 435    */
 436   private static function generate_nonce() {
 437     $mt = microtime();
 438     $rand = mt_rand();
 439
 440     return md5($mt . $rand); // md5s look nicer than numbers
 441   }
 442 }
 443
 444 class OAuthServer {
 445   protected $timestamp_threshold = 300; // in seconds, five minutes
 446   protected $version = 1.0;             // hi blaine
 447   protected $signature_methods = array();
 448
 449   protected $data_store;
 450
 451   function __construct($data_store) {
 452     $this->data_store = $data_store;
 453   }
 454
 455   public function add_signature_method($signature_method) {
 456     $this->signature_methods[$signature_method->get_name()] =
 457       $signature_method;
 458   }
 459
 460   // high level functions
 461
 462   /**
 463    * process a request_token request
 464    * returns the request token on success
 465    */
 466   public function fetch_request_token(&$request) {
 467     $this->get_version($request);
 468
 469     $consumer = $this->get_consumer($request);
 470
 471     // no token required for the initial token request
 472     $token = NULL;
 473
 474     $this->check_signature($request, $consumer, $token);
 475
 476     $new_token = $this->data_store->new_request_token($consumer);
 477
 478     return $new_token;
 479   }
 480
 481   /**
 482    * process an access_token request
 483    * returns the access token on success
 484    */
 485   public function fetch_access_token(&$request) {
 486     $this->get_version($request);
 487
 488     $consumer = $this->get_consumer($request);
 489
 490     // requires authorized request token
 491     $token = $this->get_token($request, $consumer, "request");
 492
 493
 494     $this->check_signature($request, $consumer, $token);
 495
 496     $new_token = $this->data_store->new_access_token($token, $consumer);
 497
 498     return $new_token;
 499   }
 500
 501   /**
 502    * verify an api call, checks all the parameters
 503    */
 504   public function verify_request(&$request) {
 505     global $OAuth_last_computed_signature;
 506     $OAuth_last_computed_signature = false;
 507     $this->get_version($request);
 508     $consumer = $this->get_consumer($request);
 509     $token = $this->get_token($request, $consumer, "access");
 510     $this->check_signature($request, $consumer, $token);
 511     return array($consumer, $token);
 512   }
 513
 514   // Internals from here
 515   /**
 516    * version 1
 517    */
 518   private function get_version(&$request) {
 519     $version = $request->get_parameter("oauth_version");
 520     if (!$version) {
 521       $version = 1.0;
 522     }
 523     if ($version && $version != $this->version) {
 524       throw new OAuthException("OAuth version '$version' not supported");
 525     }
 526     return $version;
 527   }
 528
 529   /**
 530    * figure out the signature with some defaults
 531    */
 532   private function get_signature_method(&$request) {
 533     $signature_method =
 534         @$request->get_parameter("oauth_signature_method");
 535     if (!$signature_method) {
 536       $signature_method = "PLAINTEXT";
 537     }
 538     if (!in_array($signature_method,
 539                   array_keys($this->signature_methods))) {
 540       throw new OAuthException(
 541         "Signature method '$signature_method' not supported " .
 542         "try one of the following: " .
 543         implode(", ", array_keys($this->signature_methods))
 544       );
 545     }
 546     return $this->signature_methods[$signature_method];
 547   }
 548
 549   /**
 550    * try to find the consumer for the provided request's consumer key
 551    */
 552   private function get_consumer(&$request) {
 553     $consumer_key = @$request->get_parameter("oauth_consumer_key");
 554     if (!$consumer_key) {
 555       throw new OAuthException("Invalid consumer key");
 556     }
 557
 558     $consumer = $this->data_store->lookup_consumer($consumer_key);
 559     if (!$consumer) {
 560       throw new OAuthException("Invalid consumer");
 561     }
 562
 563     return $consumer;
 564   }
 565
 566   /**
 567    * try to find the token for the provided request's token key
 568    */
 569   private function get_token(&$request, $consumer, $token_type="access") {
 570     $token_field = @$request->get_parameter('oauth_token');
 571     if ( !$token_field) return false;
 572     $token = $this->data_store->lookup_token(
 573       $consumer, $token_type, $token_field
 574     );
 575     if (!$token) {
 576       throw new OAuthException("Invalid $token_type token: $token_field");
 577     }
 578     return $token;
 579   }
 580
 581   /**
 582    * all-in-one function to check the signature on a request
 583    * should guess the signature method appropriately
 584    */
 585   private function check_signature(&$request, $consumer, $token) {
 586     // this should probably be in a different method
 587     global $OAuth_last_computed_signature;
 588     $OAuth_last_computed_signature = false;
 589
 590     $timestamp = @$request->get_parameter('oauth_timestamp');
 591     $nonce = @$request->get_parameter('oauth_nonce');
 592
 593     $this->check_timestamp($timestamp);
 594     $this->check_nonce($consumer, $token, $nonce, $timestamp);
 595
 596     $signature_method = $this->get_signature_method($request);
 597
 598     $signature = $request->get_parameter('oauth_signature');
 599     $valid_sig = $signature_method->check_signature(
 600       $request,
 601       $consumer,
 602       $token,
 603       $signature
 604     );
 605
 606     if (!$valid_sig) {
 607       $ex_text = "Invalid signature";
 608       if ( $OAuth_last_computed_signature ) {
 609           $ex_text = $ex_text . " ours= $OAuth_last_computed_signature yours=$signature";
 610       }
 611       throw new OAuthException($ex_text);
 612     }
 613   }
 614
 615   /**
 616    * check that the timestamp is new enough
 617    */
 618   private function check_timestamp($timestamp) {
 619     // verify that timestamp is recentish
 620     $now = time();
 621     if ($now - $timestamp > $this->timestamp_threshold) {
 622       throw new OAuthException(
 623         "Expired timestamp, yours $timestamp, ours $now"
 624       );
 625     }
 626   }
 627
 628   /**
 629    * check that the nonce is not repeated
 630    */
 631   private function check_nonce($consumer, $token, $nonce, $timestamp) {
 632     // verify that the nonce is uniqueish
 633     $found = $this->data_store->lookup_nonce(
 634       $consumer,
 635       $token,
 636       $nonce,
 637       $timestamp
 638     );
 639     if ($found) {
 640       throw new OAuthException("Nonce already used: $nonce");
 641     }
 642   }
 643
 644 }
 645
 646 class OAuthDataStore {
 647   function lookup_consumer($consumer_key) {
 648     // implement me
 649   }
 650
 651   function lookup_token($consumer, $token_type, $token) {
 652     // implement me
 653   }
 654
 655   function lookup_nonce($consumer, $token, $nonce, $timestamp) {
 656     // implement me
 657   }
 658
 659   function new_request_token($consumer) {
 660     // return a new token attached to this consumer
 661   }
 662
 663   function new_access_token($token, $consumer) {
 664     // return a new access token attached to this consumer
 665     // for the user associated with this token if the request token
 666     // is authorized
 667     // should also invalidate the request token
 668   }
 669
 670 }
 671
 672 class OAuthUtil {
 673   public static function urlencode_rfc3986($input) {
 674   if (is_array($input)) {
 675     return array_map(array('OAuthUtil', 'urlencode_rfc3986'), $input);
 676   } else if (is_scalar($input)) {
 677     return str_replace(
 678       '+',
 679       ' ',
 680       str_replace('%7E', '~', rawurlencode($input))
 681     );
 682   } else {
 683     return '';
 684   }
 685 }
 686
 687
 688   // This decode function isn't taking into consideration the above
 689   // modifications to the encoding process. However, this method doesn't
 690   // seem to be used anywhere so leaving it as is.
 691   public static function urldecode_rfc3986($string) {
 692     return urldecode($string);
 693   }
 694
 695   // Utility function for turning the Authorization: header into
 696   // parameters, has to do some unescaping
 697   // Can filter out any non-oauth parameters if needed (default behaviour)
 698   public static function split_header($header, $only_allow_oauth_parameters = true) {
 699     $pattern = '/(([-_a-z]*)=("([^"]*)"|([^,]*)),?)/';
 700     $offset = 0;
 701     $params = array();
 702     while (preg_match($pattern, $header, $matches, PREG_OFFSET_CAPTURE, $offset) > 0) {
 703       $match = $matches[0];
 704       $header_name = $matches[2][0];
 705       $header_content = (isset($matches[5])) ? $matches[5][0] : $matches[4][0];
 706       if (preg_match('/^oauth_/', $header_name) || !$only_allow_oauth_parameters) {
 707         $params[$header_name] = OAuthUtil::urldecode_rfc3986($header_content);
 708       }
 709       $offset = $match[1] + strlen($match[0]);
 710     }
 711
 712     if (isset($params['realm'])) {
 713       unset($params['realm']);
 714     }
 715
 716     return $params;
 717   }
 718
 719   // helper to try to sort out headers for people who aren't running apache
 720   public static function get_headers() {
 721     if (function_exists('apache_request_headers')) {
 722       // we need this to get the actual Authorization: header
 723       // because apache tends to tell us it doesn't exist
 724       return apache_request_headers();
 725     }
 726     // otherwise we don't have apache and are just going to have to hope
 727     // that $_SERVER actually contains what we need
 728     $out = array();
 729     foreach ($_SERVER as $key => $value) {
 730       if (substr($key, 0, 5) == "HTTP_") {
 731         // this is chaos, basically it is just there to capitalize the first
 732         // letter of every word that is not an initial HTTP and strip HTTP
 733         // code from przemek
 734         $key = str_replace(
 735           " ",
 736           "-",
 737           ucwords(strtolower(str_replace("_", " ", substr($key, 5))))
 738         );
 739         $out[$key] = $value;
 740       }
 741     }
 742     return $out;
 743   }
 744
 745   // This function takes a input like a=b&a=c&d=e and returns the parsed
 746   // parameters like this
 747   // array('a' => array('b','c'), 'd' => 'e')
 748   public static function parse_parameters( $input ) {
 749     if (!isset($input) || !$input) return array();
 750
 751     $pairs = explode('&', $input);
 752
 753     $parsed_parameters = array();
 754     foreach ($pairs as $pair) {
 755       $split = explode('=', $pair, 2);
 756       $parameter = OAuthUtil::urldecode_rfc3986($split[0]);
 757       $value = isset($split[1]) ? OAuthUtil::urldecode_rfc3986($split[1]) : '';
 758
 759       if (isset($parsed_parameters[$parameter])) {
 760         // We have already recieved parameter(s) with this name, so add to the list
 761         // of parameters with this name
 762
 763         if (is_scalar($parsed_parameters[$parameter])) {
 764           // This is the first duplicate, so transform scalar (string) into an array
 765           // so we can add the duplicates
 766           $parsed_parameters[$parameter] = array($parsed_parameters[$parameter]);
 767         }
 768
 769         $parsed_parameters[$parameter][] = $value;
 770       } else {
 771         $parsed_parameters[$parameter] = $value;
 772       }
 773     }
 774     return $parsed_parameters;
 775   }
 776
 777   public static function build_http_query($params) {
 778     if (!$params) return '';
 779
 780     // Urlencode both keys and values
 781     $keys = OAuthUtil::urlencode_rfc3986(array_keys($params));
 782     $values = OAuthUtil::urlencode_rfc3986(array_values($params));
 783     $params = array_combine($keys, $values);
 784
 785     // Parameters are sorted by name, using lexicographical byte value ordering.
 786     // Ref: Spec: 9.1.1 (1)
 787     uksort($params, 'strcmp');
 788
 789     $pairs = array();
 790     foreach ($params as $parameter => $value) {
 791       if (is_array($value)) {
 792         // If two or more parameters share the same name, they are sorted by their value
 793         // Ref: Spec: 9.1.1 (1)
 794         natsort($value);
 795         foreach ($value as $duplicate_value) {
 796           $pairs[] = $parameter . '=' . $duplicate_value;
 797         }
 798       } else {
 799         $pairs[] = $parameter . '=' . $value;
 800       }
 801     }
 802     // For each parameter, the name is separated from the corresponding value by an '=' character (ASCII code 61)
 803     // Each name-value pair is separated by an '&' character (ASCII code 38)
 804     return implode('&', $pairs);
 805   }
 806 }
 807
 808 ?>