<?php

// vim: foldmethod=marker

/* Generic exception class
 */
if ( !class_exists( 'OAuthException' ) ) {

  class OAuthException extends Exception {

    // pass

  }

}

if ( !class_exists( 'OAuthConsumer' ) ) {

  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]";

    }

  }

}
if ( !class_exists( 'OAuthToken' ) ) {

  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
 */
if ( !class_exists( 'OAuthSignatureMethod' ) ) {

  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")
 */
if ( !class_exists( 'OAuthSignatureMethod_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")
 */
if ( !class_exists( 'OAuthSignatureMethod_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")
 */
if ( !class_exists( 'OAuthSignatureMethod_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;

    }

  }

}
if ( !class_exists( 'OAuthRequest' ) ) {

  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

    }

  }

}
if ( !class_exists( 'OAuthServer' ) ) {

  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" );
      }

    }

  }

}

if ( !class_exists( 'OAuthDataStore' ) ) {

  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

    }

  }

}

if ( !class_exists( 'OAuthUtil' ) ) {

  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 );

    }

  }

}