miniblog

OAuth.php (26482B)

---

 <?php
 // vim: foldmethod=marker
 
 /* Generic exception class
  */
 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);
     return $built == $signature;
   }
 }
 
 /**
  * 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 {
   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();
     $parameters = array_merge( OAuthUtil::parse_parameters(parse_url($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']) || $_SERVER['HTTPS'] != "on")
               ? 'http'
               : 'https';
     @$http_url or $http_url = $scheme .
                               '://' . $_SERVER['HTTP_HOST'] .
                               ':' .
                               $_SERVER['SERVER_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']);
 
       // It's a POST request of the proper content-type, so parse POST
       // parameters and add those overriding any duplicates from GET
       if ($http_method == "POST"
           && @strstr($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 (@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();
     $defaults = array("oauth_version" => OAuthRequest::$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);
 
     $port = @$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($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->get_parameter("oauth_signature_method");
 
     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->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');
     $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->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) {
       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)
   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] = OAuthUtil::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
       $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)
         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);
   }
 }
 
 ?>