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<?php

/**

 * JSON Web Token implementation, based on this spec:

 * http://tools.ietf.org/html/draft-ietf-oauth-json-web-token-06

 *

 * PHP version 5

 *

 * @category Authentication

 * @package  Authentication_JWT

 * @author   Neuman Vong <neuman@twilio.com>

 * @author   Anant Narayanan <anant@php.net>

 * @license  http://opensource.org/licenses/BSD-3-Clause 3-clause BSD

 * @link     https://github.com/firebase/php-jwt

 */

class JWT

{

    public static $supported_algs = array(

        'HS256' => array('hash_hmac', 'SHA256'),

        'HS512' => array('hash_hmac', 'SHA512'),

        'HS384' => array('hash_hmac', 'SHA384'),

        'RS256' => array('openssl', 'SHA256'),

    );

    /**

     * Decodes a JWT string into a PHP object.

     *

     * @param string      $jwt           The JWT

     * @param string|Array|null $key     The secret key, or map of keys

     * @param Array       $allowed_algs  List of supported verification algorithms

     *

     * @return object      The JWT's payload as a PHP object

     *

     * @throws DomainException              Algorithm was not provided

     * @throws UnexpectedValueException     Provided JWT was invalid

     * @throws SignatureInvalidException    Provided JWT was invalid because the signature verification failed

     * @throws BeforeValidException         Provided JWT is trying to be used before it's eligible as defined by 'nbf'

     * @throws BeforeValidException         Provided JWT is trying to be used before it's been created as defined by 'iat'

     * @throws ExpiredException             Provided JWT has since expired, as defined by the 'exp' claim

     *

     * @uses jsonDecode

     * @uses urlsafeB64Decode

     */

    public static function decode($jwt, $key = null, $allowed_algs = array())

    {

        $tks = explode('.', $jwt);

        if (count($tks) != 3) {

            throw new UnexpectedValueException('Wrong number of segments');

        }

        list($headb64, $bodyb64, $cryptob64) = $tks;

        if (null === ($header = JWT::jsonDecode(JWT::urlsafeB64Decode($headb64)))) {

            throw new UnexpectedValueException('Invalid header encoding');

        }

        if (null === $payload = JWT::jsonDecode(JWT::urlsafeB64Decode($bodyb64))) {

            throw new UnexpectedValueException('Invalid claims encoding');

        }

        $sig = JWT::urlsafeB64Decode($cryptob64);

        if (isset($key)) {

            if (empty($header->alg)) {

                throw new DomainException('Empty algorithm');

            }

            if (empty(self::$supported_algs[$header->alg])) {

                throw new DomainException('Algorithm not supported');

            }

            if (!is_array($allowed_algs) || !in_array($header->alg, $allowed_algs)) {

                throw new DomainException('Algorithm not allowed');

            }

            if (is_array($key)) {

                if (isset($header->kid)) {

                    $key = $key[$header->kid];

                } else {

                    throw new DomainException('"kid" empty, unable to lookup correct key');

                }

            }

            // Check the signature

            if (!JWT::verify("$headb64.$bodyb64", $sig, $key, $header->alg)) {

                throw new SignatureInvalidException('Signature verification failed');

            }

            // Check if the nbf if it is defined. This is the time that the

            // token can actually be used. If it's not yet that time, abort.

            if (isset($payload->nbf) && $payload->nbf > time()) {

                throw new BeforeValidException(

                    'Cannot handle token prior to ' . date(DateTime::ISO8601, $payload->nbf)

                );

            }

            // Check that this token has been created before 'now'. This prevents

            // using tokens that have been created for later use (and haven't

            // correctly used the nbf claim).

            if (isset($payload->iat) && $payload->iat > time()) {

                throw new BeforeValidException(

                    'Cannot handle token prior to ' . date(DateTime::ISO8601, $payload->iat)

                );

            }

            // Check if this token has expired.

            if (isset($payload->exp) && time() >= $payload->exp) {

                throw new ExpiredException('Expired token');

            }

        }

        return $payload;

    }

    /**

     * Converts and signs a PHP object or array into a JWT string.

     *

     * @param object|array $payload PHP object or array

     * @param string       $key     The secret key

     * @param string       $alg     The signing algorithm. Supported

     *                              algorithms are 'HS256', 'HS384' and 'HS512'

     *

     * @return string      A signed JWT

     * @uses jsonEncode

     * @uses urlsafeB64Encode

     */

    public static function encode($payload, $key, $alg = 'HS256', $keyId = null)

    {

        $header = array('typ' => 'JWT', 'alg' => $alg);

        if ($keyId !== null) {

            $header['kid'] = $keyId;

        }

        $segments = array();

        $segments[] = JWT::urlsafeB64Encode(JWT::jsonEncode($header));

        $segments[] = JWT::urlsafeB64Encode(JWT::jsonEncode($payload));

        $signing_input = implode('.', $segments);

        $signature = JWT::sign($signing_input, $key, $alg);

        $segments[] = JWT::urlsafeB64Encode($signature);

        return implode('.', $segments);

    }

    /**

     * Sign a string with a given key and algorithm.

     *

     * @param string $msg          The message to sign

     * @param string|resource $key The secret key

     * @param string $alg       The signing algorithm. Supported algorithms

     *                               are 'HS256', 'HS384', 'HS512' and 'RS256'

     *

     * @return string          An encrypted message

     * @throws DomainException Unsupported algorithm was specified

     */

    public static function sign($msg, $key, $alg = 'HS256')

    {

        if (empty(self::$supported_algs[$alg])) {

            throw new DomainException('Algorithm not supported');

        }

        list($function, $algorithm) = self::$supported_algs[$alg];

        switch($function) {

            case 'hash_hmac':

                return hash_hmac($algorithm, $msg, $key, true);

            case 'openssl':

                $signature = '';

                $success = openssl_sign($msg, $signature, $key, $algorithm);

                if (!$success) {

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

                } else {

                    return $signature;

                }

        }

    }

    /**

     * Verify a signature with the mesage, key and method. Not all methods

     * are symmetric, so we must have a separate verify and sign method.

     * @param string $msg the original message

     * @param string $signature

     * @param string|resource $key for HS*, a string key works. for RS*, must be a resource of an openssl public key

     * @param string $alg

     * @return bool

     * @throws DomainException Invalid Algorithm or OpenSSL failure

     */

    private static function verify($msg, $signature, $key, $alg)

    {

        if (empty(self::$supported_algs[$alg])) {

            throw new DomainException('Algorithm not supported');

        }

        list($function, $algorithm) = self::$supported_algs[$alg];

        switch($function) {

            case 'openssl':

                $success = openssl_verify($msg, $signature, $key, $algorithm);

                if (!$success) {

                    throw new DomainException("OpenSSL unable to verify data: " . openssl_error_string());

                } else {

                    return $signature;

                }

            case 'hash_hmac':

            default:

                $hash = hash_hmac($algorithm, $msg, $key, true);

                if (function_exists('hash_equals')) {

                    return hash_equals($signature, $hash);

                }

                $len = min(self::safeStrlen($signature), self::safeStrlen($hash));

                $status = 0;

                for ($i = 0; $i < $len; $i++) {

                    $status |= (ord($signature[$i]) ^ ord($hash[$i]));

                }

                $status |= (self::safeStrlen($signature) ^ self::safeStrlen($hash));

                return ($status === 0);

        }

    }

    /**

     * Decode a JSON string into a PHP object.

     *

     * @param string $input JSON string

     *

     * @return object          Object representation of JSON string

     * @throws DomainException Provided string was invalid JSON

     */

    public static function jsonDecode($input)

    {

        if (version_compare(PHP_VERSION, '5.4.0', '>=') && !(defined('JSON_C_VERSION') && PHP_INT_SIZE > 4)) {

            /** In PHP >=5.4.0, json_decode() accepts an options parameter, that allows you

             * to specify that large ints (like Steam Transaction IDs) should be treated as

             * strings, rather than the PHP default behaviour of converting them to floats.

             */

            $obj = json_decode($input, false, 512, JSON_BIGINT_AS_STRING);

        } else {

            /** Not all servers will support that, however, so for older versions we must

             * manually detect large ints in the JSON string and quote them (thus converting

             *them to strings) before decoding, hence the preg_replace() call.

             */

            $max_int_length = strlen((string) PHP_INT_MAX) - 1;

            $json_without_bigints = preg_replace('/:\s*(-?\d{'.$max_int_length.',})/', ': "$1"', $input);

            $obj = json_decode($json_without_bigints);

        }

        if (function_exists('json_last_error') && $errno = json_last_error()) {

            JWT::handleJsonError($errno);

        } elseif ($obj === null && $input !== 'null') {

            throw new DomainException('Null result with non-null input');

        }

        return $obj;

    }

    /**

     * Encode a PHP object into a JSON string.

     *

     * @param object|array $input A PHP object or array

     *

     * @return string          JSON representation of the PHP object or array

     * @throws DomainException Provided object could not be encoded to valid JSON

     */

    public static function jsonEncode($input)

    {

        $json = json_encode($input);

        if (function_exists('json_last_error') && $errno = json_last_error()) {

            JWT::handleJsonError($errno);

        } elseif ($json === 'null' && $input !== null) {

            throw new DomainException('Null result with non-null input');

        }

        return $json;

    }

    /**

     * Decode a string with URL-safe Base64.

     *

     * @param string $input A Base64 encoded string

     *

     * @return string A decoded string

     */

    public static function urlsafeB64Decode($input)

    {

        $remainder = strlen($input) % 4;

        if ($remainder) {

            $padlen = 4 - $remainder;

            $input .= str_repeat('=', $padlen);

        }

        return base64_decode(strtr($input, '-_', '+/'));

    }

    /**

     * Encode a string with URL-safe Base64.

     *

     * @param string $input The string you want encoded

     *

     * @return string The base64 encode of what you passed in

     */

    public static function urlsafeB64Encode($input)

    {

        return str_replace('=', '', strtr(base64_encode($input), '+/', '-_'));

    }

    /**

     * Helper method to create a JSON error.

     *

     * @param int $errno An error number from json_last_error()

     *

     * @return void

     */

    private static function handleJsonError($errno)

    {

        $messages = array(

            JSON_ERROR_DEPTH => 'Maximum stack depth exceeded',

            JSON_ERROR_CTRL_CHAR => 'Unexpected control character found',

            JSON_ERROR_SYNTAX => 'Syntax error, malformed JSON'

        );

        throw new DomainException(

            isset($messages[$errno])

            ? $messages[$errno]

            : 'Unknown JSON error: ' . $errno

        );

    }

    /**

     * Get the number of bytes in cryptographic strings.

     *

     * @param string

     * @return int

     */

    private static function safeStrlen($str)

    {

        if (function_exists('mb_strlen')) {

            return mb_strlen($str, '8bit');

        }

        return strlen($str);

    }

}