<?php

/**
 *
 * Copyright MITRE 2017
 *
 * OpenIDConnectClient for PHP5
 * Author: Michael Jett <mjett@mitre.org>
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may
 * not use this file except in compliance with the License. You may obtain
 * a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 */

namespace Jumbojett;

/**
 * Use session to manage a nonce
 */
if (!isset($_SESSION)) {
    @session_start();
}

/**
 *
 * JWT signature verification support by Jonathan Reed <jdreed@mit.edu>
 * Licensed under the same license as the rest of this file.
 *
 * phpseclib is required to validate the signatures of some tokens.
 * It can be downloaded from: http://phpseclib.sourceforge.net/
 */


/**
 * A wrapper around base64_decode which decodes Base64URL-encoded data,
 * which is not the same alphabet as base64.
 */
function base64url_decode($base64url) {
    return base64_decode(b64url2b64($base64url));
}

/**
 * Per RFC4648, "base64 encoding with URL-safe and filename-safe
 * alphabet".  This just replaces characters 62 and 63.  None of the
 * reference implementations seem to restore the padding if necessary,
 * but we'll do it anyway.
 *
 */
function b64url2b64($base64url) {
    // "Shouldn't" be necessary, but why not
    $padding = strlen($base64url) % 4;
    if ($padding > 0) {
	$base64url .= str_repeat("=", 4 - $padding);
    }
    return strtr($base64url, '-_', '+/');
}


/**
 * OpenIDConnect Exception Class
 */
class OpenIDConnectClientException extends \Exception
{

}

/**
 * Require the CURL and JSON PHP extentions to be installed
 */
if (!function_exists('curl_init')) {
    throw new OpenIDConnectClientException('OpenIDConnect needs the CURL PHP extension.');
}
if (!function_exists('json_decode')) {
    throw new OpenIDConnectClientException('OpenIDConnect needs the JSON PHP extension.');
}

/**
 *
 * Please note this class stores nonces by default in $_SESSION['openid_connect_nonce']
 *
 */
class OpenIDConnectClient
{

    /**
     * @var string arbitrary id value
     */
    private $clientID;

    /*
     * @var string arbitrary name value
     */
    private $clientName;

    /**
     * @var string arbitrary secret value
     */
    private $clientSecret;

    /**
     * @var array holds the provider configuration
     */
    private $providerConfig = array();

    /**
     * @var string http proxy if necessary
     */
    private $httpProxy;

    /**
     * @var string full system path to the SSL certificate
     */
    private $certPath;

    /**
     * @var bool Verify SSL peer on transactions
     */
    private $verifyPeer = true;

    /**
     * @var bool Verify peer hostname on transactions
     */
    private $verifyHost = true;

    /**
     * @var string if we aquire an access token it will be stored here
     */
    private $accessToken;

    /**
     * @var string if we aquire a refresh token it will be stored here
     */
    private $refreshToken;

    /**
     * @var string if we acquire an id token it will be stored here
     */
    private $idToken;

    /**
     * @var string stores the token response
     */
    private $tokenResponse;

    /**
     * @var array holds scopes
     */
    private $scopes = array();

    /**
     * @var int|null Response code from the server
     */
    private $responseCode = null;

    /**
     * @var array holds response types
     */
    private $responseTypes = array();

    /**
     * @var array holds a cache of info returned from the user info endpoint
     */
    private $userInfo = array();

    /**
     * @var array holds authentication parameters
     */
    private $authParams = array();

    /**
     * @var mixed holds well-known openid server properties
     */
    private $wellKnown = false;

    /**
     * @var int timeout (seconds)
     */
    protected $timeOut = 60;

    /**
     * @param $provider_url string optional
     *
     * @param $client_id string optional
     * @param $client_secret string optional
     *
     */
    public function __construct($provider_url = null, $client_id = null, $client_secret = null) {
        $this->setProviderURL($provider_url);
        $this->clientID = $client_id;
        $this->clientSecret = $client_secret;
    }

    /**
     * @param $provider_url
     */
    public function setProviderURL($provider_url) {
        $this->providerConfig['issuer'] = $provider_url;
    }

    /**
     * @param $response_types
     */
    public function setResponseTypes($response_types) {
        $this->responseTypes = array_merge($this->responseTypes, (array)$response_types);
    }

    /**
     * @return bool
     * @throws OpenIDConnectClientException
     */
    public function authenticate() {

        // Do a preemptive check to see if the provider has thrown an error from a previous redirect
        if (isset($_REQUEST['error'])) {
            $desc = isset($_REQUEST['error_description']) ? " Description: " . $_REQUEST['error_description'] : "";
            throw new OpenIDConnectClientException("Error: " . $_REQUEST['error'] .$desc);
        }

        // If we have an authorization code then proceed to request a token
        if (isset($_REQUEST["code"])) {

            $code = $_REQUEST["code"];
            $token_json = $this->requestTokens($code);

            // Throw an error if the server returns one
            if (isset($token_json->error)) {
                if (isset($token_json->error_description)) {
                    throw new OpenIDConnectClientException($token_json->error_description);
                }
                throw new OpenIDConnectClientException('Got response: ' . $token_json->error);
            }

            // Do an OpenID Connect session check
            if ($_REQUEST['state'] != $this->getState()) {
                throw new OpenIDConnectClientException("Unable to determine state");
            }

	    // Cleanup state
	    $this->unsetState();

            if (!property_exists($token_json, 'id_token')) {
                throw new OpenIDConnectClientException("User did not authorize openid scope.");
            }

            $claims = $this->decodeJWT($token_json->id_token, 1);

            // Verify the signature
            if ($this->canVerifySignatures()) {
		if (!$this->getProviderConfigValue('jwks_uri')) {
                    throw new OpenIDConnectClientException ("Unable to verify signature due to no jwks_uri being defined");
                }
                if (!$this->verifyJWTsignature($token_json->id_token)) {
                    throw new OpenIDConnectClientException ("Unable to verify signature");
                }
            } else {
                user_error("Warning: JWT signature verification unavailable.");
            }

            // If this is a valid claim
            if ($this->verifyJWTclaims($claims, $token_json->access_token)) {

                // Clean up the session a little
                $this->unsetNonce();

		// Save the full response
                $this->tokenResponse = $token_json;

                // Save the id token
                $this->idToken = $token_json->id_token;

                // Save the access token
                $this->accessToken = $token_json->access_token;

                // Save the refresh token, if we got one
                if (isset($token_json->refresh_token)) $this->refreshToken = $token_json->refresh_token;

                // Success!
                return true;

            } else {
                throw new OpenIDConnectClientException ("Unable to verify JWT claims");
            }

        } else {

            $this->requestAuthorization();
            return false;
        }

    }

    /**
     * It calls the end-session endpoint of the OpenID Connect provider to notify the OpenID
     * Connect provider that the end-user has logged out of the relying party site
     * (the client application).
     *
     * @param string $accessToken ID token (obtained at login)
     * @param string $redirect URL to which the RP is requesting that the End-User's User Agent
     * be redirected after a logout has been performed. The value MUST have been previously
     * registered with the OP. Value can be null.
     *
     */
    public function signOut($accessToken, $redirect) {
        $signout_endpoint = $this->getProviderConfigValue("end_session_endpoint");

        $signout_params = null;
        if($redirect == null){
          $signout_params = array('id_token_hint' => $accessToken);
        }
        else {
          $signout_params = array(
                'id_token_hint' => $accessToken,
                'post_logout_redirect_uri' => $redirect);
        }

        $signout_endpoint  .= (strpos($signout_endpoint, '?') === false ? '?' : '&') . http_build_query( $signout_params, null, '&');
        $this->redirect($signout_endpoint);
    }

    /**
     * @param $scope - example: openid, given_name, etc...
     */
    public function addScope($scope) {
        $this->scopes = array_merge($this->scopes, (array)$scope);
    }

    /**
     * @param $param - example: prompt=login
     */
    public function addAuthParam($param) {
        $this->authParams = array_merge($this->authParams, (array)$param);
    }

    /**
     * Get's anything that we need configuration wise including endpoints, and other values
     *
     * @param $param
     * @param string $default optional
     * @throws OpenIDConnectClientException
     * @return string
     *
     */
    private function getProviderConfigValue($param, $default = null) {

        // If the configuration value is not available, attempt to fetch it from a well known config endpoint
        // This is also known as auto "discovery"
        if (!isset($this->providerConfig[$param])) {
	    if(!$this->wellKnown){
            	$well_known_config_url = rtrim($this->getProviderURL(),"/") . "/.well-known/openid-configuration";
            	$this->wellKnown = json_decode($this->fetchURL($well_known_config_url));
	    }

	    $value = false;
	    if(isset($this->wellKnown->{$param})){
                $value = $this->wellKnown->{$param};
            }

            if ($value) {
                $this->providerConfig[$param] = $value;
            } elseif(isset($default)) {
                // Uses default value if provided
                $this->providerConfig[$param] = $default;
            } else {
                throw new OpenIDConnectClientException("The provider {$param} has not been set. Make sure your provider has a well known configuration available.");
            }

        }

        return $this->providerConfig[$param];
    }


    /**
     * @param string $url Sets redirect URL for auth flow
     */
    public function setRedirectURL ($url) {
        if (parse_url($url,PHP_URL_HOST) !== false) {
            $this->redirectURL = $url;
        }
    }

    /**
     * Gets the URL of the current page we are on, encodes, and returns it
     *
     * @return string
     */
    public function getRedirectURL() {

        // If the redirect URL has been set then return it.
        if (property_exists($this, 'redirectURL') && $this->redirectURL) {
            return $this->redirectURL;
        }

        // Other-wise return the URL of the current page

        /**
         * Thank you
         * http://stackoverflow.com/questions/189113/how-do-i-get-current-page-full-url-in-php-on-a-windows-iis-server
         */

        /*
         * Compatibility with multiple host headers.
         * The problem with SSL over port 80 is resolved and non-SSL over port 443.
         * Support of 'ProxyReverse' configurations.
         */

        if (isset($_SERVER["HTTP_UPGRADE_INSECURE_REQUESTS"]) && ($_SERVER['HTTP_UPGRADE_INSECURE_REQUESTS'] == 1)) {
            $protocol = 'https';
        } else {
            $protocol = @$_SERVER['HTTP_X_FORWARDED_PROTO']
                ?: @$_SERVER['REQUEST_SCHEME']
                ?: ((isset($_SERVER["HTTPS"]) && $_SERVER["HTTPS"] == "on") ? "https" : "http");
        }

        $port = @intval($_SERVER['HTTP_X_FORWARDED_PORT'])
              ?: @intval($_SERVER["SERVER_PORT"])
              ?: (($protocol === 'https') ? 443 : 80);

        $host = @explode(":", $_SERVER['HTTP_HOST'])[0]
              ?: @$_SERVER['SERVER_NAME']
              ?: @$_SERVER['SERVER_ADDR'];

        $port = (443 == $port) || (80 == $port) ? '' : ':' . $port;

        return sprintf('%s://%s%s/%s', $protocol, $host, $port, @trim(reset(explode("?", $_SERVER['REQUEST_URI'])), '/'));
    }

    /**
     * Used for arbitrary value generation for nonces and state
     *
     * @return string
     */
    protected function generateRandString() {
        return md5(uniqid(rand(), TRUE));
    }

    /**
     * Start Here
     * @return void
     */
    private function requestAuthorization() {

        $auth_endpoint = $this->getProviderConfigValue("authorization_endpoint");
        $response_type = "code";

        // Generate and store a nonce in the session
        // The nonce is an arbitrary value
        $nonce = $this->setNonce($this->generateRandString());

        // State essentially acts as a session key for OIDC
        $state = $this->setState($this->generateRandString());

        $auth_params = array_merge($this->authParams, array(
            'response_type' => $response_type,
            'redirect_uri' => $this->getRedirectURL(),
            'client_id' => $this->clientID,
            'nonce' => $nonce,
            'state' => $state,
            'scope' => 'openid'
        ));

        // If the client has been registered with additional scopes
        if (!empty($this->scopes)) {
            $auth_params = array_merge($auth_params, array('scope' => implode(' ', $this->scopes)));
        }

        // If the client has been registered with additional response types
        if (!empty($this->responseTypes)) {
            $auth_params = array_merge($auth_params, array('response_type' => implode(' ', $this->responseTypes)));
        }

        $auth_endpoint .= (strpos($auth_endpoint, '?') === false ? '?' : '&') . http_build_query($auth_params, null, '&');

        session_commit();
        $this->redirect($auth_endpoint);
    }

    /**
     * Requests a client credentials token
     *
     */
    public function requestClientCredentialsToken() {
        $token_endpoint = $this->getProviderConfigValue("token_endpoint");

        $headers = [];

        $grant_type = "client_credentials";

        $post_data = array(
            'grant_type'    => $grant_type,
            'client_id'     => $this->clientID,
            'client_secret' => $this->clientSecret,
            'scope'         => implode(' ', $this->scopes)
        );

        // Convert token params to string format
        $post_params = http_build_query($post_data, null, '&');

        return json_decode($this->fetchURL($token_endpoint, $post_params, $headers));
    }


 /**
     * Requests a resource owner token
     * (Defined in https://tools.ietf.org/html/rfc6749#section-4.3)
     * 
     * @param $bClientAuth boolean Indicates that the Client ID and Secret be used for client authentication
     */
    public function requestResourceOwnerToken($bClientAuth =  FALSE) {
        $token_endpoint = $this->getProviderConfigValue("token_endpoint");

        $headers = [];

        $grant_type = "password";

        $post_data = array(
            'grant_type'    => $grant_type,
            'username'      => $this->authParams['username'],
            'password'      => $this->authParams['password'],
            'scope'         => implode(' ', $this->scopes)
        );

        //For client authentication include the client values
        if($bClientAuth) {
            $post_data['client_id']     = $this->clientID;
            $post_data['client_secret'] = $this->clientSecret;
        }

        // Convert token params to string format
        $post_params = http_build_query($post_data, null, '&');

        return json_decode($this->fetchURL($token_endpoint, $post_params, $headers));
    }


    /**
     * Requests ID and Access tokens
     *
     * @param $code
     * @return mixed
     */
    private function requestTokens($code) {
        $token_endpoint = $this->getProviderConfigValue("token_endpoint");
        $token_endpoint_auth_methods_supported = $this->getProviderConfigValue("token_endpoint_auth_methods_supported", ['client_secret_basic']);

        $headers = [];

        $grant_type = "authorization_code";

        $token_params = array(
            'grant_type' => $grant_type,
            'code' => $code,
            'redirect_uri' => $this->getRedirectURL(),
            'client_id' => $this->clientID,
            'client_secret' => $this->clientSecret
        );

        # Consider Basic authentication if provider config is set this way
        if (in_array('client_secret_basic', $token_endpoint_auth_methods_supported)) {
            $headers = ['Authorization: Basic ' . base64_encode($this->clientID . ':' . $this->clientSecret)];
            unset($token_params['client_secret']);
        }

        // Convert token params to string format
        $token_params = http_build_query($token_params, null, '&');

        return json_decode($this->fetchURL($token_endpoint, $token_params, $headers));

    }

    /**
     * Requests Access token with refresh token
     *
     * @param $code
     * @return mixed
     */
    public function refreshToken($refresh_token) {
        $token_endpoint = $this->getProviderConfigValue("token_endpoint");

        $grant_type = "refresh_token";

        $token_params = array(
            'grant_type' => $grant_type,
            'refresh_token' => $refresh_token,
            'client_id' => $this->clientID,
            'client_secret' => $this->clientSecret,
        );

        // Convert token params to string format
        $token_params = http_build_query($token_params, null, '&');

        $json = json_decode($this->fetchURL($token_endpoint, $token_params));
        $this->refreshToken = $json->refresh_token;

        return $json;
    }

    /**
      * @param array $keys
      * @param array $header
      * @throws OpenIDConnectClientException
      * @return object
      */
     private function get_key_for_header($keys, $header) {
         foreach ($keys as $key) {
             if ($key->kty == 'RSA') {
                 if (!isset($header->kid) || $key->kid == $header->kid) {
                     return $key;
                 }
             } else {
                 if ($key->alg == $header->alg && $key->kid == $header->kid) {
                     return $key;
                 }
             }
         }
         if (isset($header->kid)) {
             throw new OpenIDConnectClientException('Unable to find a key for (algorithm, kid):' . $header->alg . ', ' . $header->kid . ')');
         } else {
             throw new OpenIDConnectClientException('Unable to find a key for RSA');
         }
     }


    /**
     * @param string $hashtype
     * @param object $key
     * @throws OpenIDConnectClientException
     * @return bool
     */
    private function verifyRSAJWTsignature($hashtype, $key, $payload, $signature) {
        if (!class_exists('\phpseclib\Crypt\RSA') && !class_exists('Crypt_RSA')) {
            throw new OpenIDConnectClientException('Crypt_RSA support unavailable.');
        }
        if (!(property_exists($key, 'n') and property_exists($key, 'e'))) {
            throw new OpenIDConnectClientException('Malformed key object');
        }

        /* We already have base64url-encoded data, so re-encode it as
           regular base64 and use the XML key format for simplicity.
        */
        $public_key_xml = "<RSAKeyValue>\r\n".
            "  <Modulus>" . b64url2b64($key->n) . "</Modulus>\r\n" .
            "  <Exponent>" . b64url2b64($key->e) . "</Exponent>\r\n" .
            "</RSAKeyValue>";
	if(class_exists('Crypt_RSA')) {
        	$rsa = new Crypt_RSA();
		$rsa->setHash($hashtype);
        	$rsa->loadKey($public_key_xml, Crypt_RSA::PUBLIC_FORMAT_XML);
        	$rsa->signatureMode = Crypt_RSA::SIGNATURE_PKCS1;
	} else {
		$rsa = new \phpseclib\Crypt\RSA();
		$rsa->setHash($hashtype);
        	$rsa->loadKey($public_key_xml, \phpseclib\Crypt\RSA::PUBLIC_FORMAT_XML);
        	$rsa->signatureMode = \phpseclib\Crypt\RSA::SIGNATURE_PKCS1;
	}
        return $rsa->verify($payload, $signature);
    }
	
    /**
     * @param string $hashtype
     * @param object $key
     * @throws OpenIDConnectClientException
     * @return bool
     */
    private function verifyHMACJWTsignature($hashtype, $key, $payload, $signature)
    {
        if (!function_exists('hash_hmac')) {
            throw new OpenIDConnectClientException('hash_hmac support unavailable.');
        }

        $expected=hash_hmac($hashtype, $payload, $key, true);

        if (function_exists('hash_equals')) {
            return hash_equals($signature, $expected);
        } else {
            return self::hashEquals($signature, $expected);
        }
    }

    /**
     * @param $jwt string encoded JWT
     * @throws OpenIDConnectClientException
     * @return bool
     */
    private function verifyJWTsignature($jwt) {
        $parts = explode(".", $jwt);
        $signature = base64url_decode(array_pop($parts));
        $header = json_decode(base64url_decode($parts[0]));
        $payload = implode(".", $parts);
        $jwks = json_decode($this->fetchURL($this->getProviderConfigValue('jwks_uri')));
        if ($jwks === NULL) {
            throw new OpenIDConnectClientException('Error decoding JSON from jwks_uri');
        }
        $verified = false;
        switch ($header->alg) {
        case 'RS256':
        case 'RS384':
        case 'RS512':
            $hashtype = 'sha' . substr($header->alg, 2);

            $verified = $this->verifyRSAJWTsignature($hashtype,
                                                     $this->get_key_for_header($jwks->keys, $header),
                                                     $payload, $signature);
            break;
	case 'HS256':
        case 'HS512':
        case 'HS384':
            $hashtype = 'SHA' . substr($header->alg, 2);
            $verified = $this->verifyHMACJWTsignature($hashtype, $this->getClientSecret(), $payload, $signature);
            break;		
        default:
            throw new OpenIDConnectClientException('No support for signature type: ' . $header->alg);
        }
        return $verified;
    }

    /**
     * @param object $claims
     * @return bool
     */
    private function verifyJWTclaims($claims, $accessToken = null) {
	if(isset($claims->at_hash) && isset($accessToken)){
            if(isset($this->getAccessTokenHeader()->alg) && $this->getAccessTokenHeader()->alg != 'none'){
                $bit = substr($this->getAccessTokenHeader()->alg, 2, 3);
            }else{
                // TODO: Error case. throw exception???
                $bit = '256';
            }
            $len = ((int)$bit)/16;
            $expecte_at_hash = $this->urlEncode(substr(hash('sha'.$bit, $accessToken, true), 0, $len));
        }
        return (($claims->iss == $this->getProviderURL())
            && (($claims->aud == $this->clientID) || (in_array($this->clientID, $claims->aud)))
            && ($claims->nonce == $this->getNonce())
            && ( !isset($claims->exp) || $claims->exp >= time())
            && ( !isset($claims->nbf) || $claims->nbf <= time())
            && ( !isset($claims->at_hash) || $claims->at_hash == $expecte_at_hash )
        );
    }

    /**
     * @param string $str
     * @return string
     */
    protected function urlEncode($str) {
        $enc = base64_encode($str);
        $enc = rtrim($enc, "=");
        $enc = strtr($enc, "+/", "-_");
        return $enc;
    }

    /**
     * @param $jwt string encoded JWT
     * @param int $section the section we would like to decode
     * @return object
     */
    private function decodeJWT($jwt, $section = 0) {

        $parts = explode(".", $jwt);
        return json_decode(base64url_decode($parts[$section]));
    }

    /**
     *
     * @param $attribute string optional
     *
     * Attribute        Type    Description
     * user_id            string    REQUIRED Identifier for the End-User at the Issuer.
     * name            string    End-User's full name in displayable form including all name parts, ordered according to End-User's locale and preferences.
     * given_name        string    Given name or first name of the End-User.
     * family_name        string    Surname or last name of the End-User.
     * middle_name        string    Middle name of the End-User.
     * nickname        string    Casual name of the End-User that may or may not be the same as the given_name. For instance, a nickname value of Mike might be returned alongside a given_name value of Michael.
     * profile            string    URL of End-User's profile page.
     * picture            string    URL of the End-User's profile picture.
     * website            string    URL of End-User's web page or blog.
     * email            string    The End-User's preferred e-mail address.
     * verified        boolean    True if the End-User's e-mail address has been verified; otherwise false.
     * gender            string    The End-User's gender: Values defined by this specification are female and male. Other values MAY be used when neither of the defined values are applicable.
     * birthday        string    The End-User's birthday, represented as a date string in MM/DD/YYYY format. The year MAY be 0000, indicating that it is omitted.
     * zoneinfo        string    String from zoneinfo [zoneinfo] time zone database. For example, Europe/Paris or America/Los_Angeles.
     * locale            string    The End-User's locale, represented as a BCP47 [RFC5646] language tag. This is typically an ISO 639-1 Alpha-2 [ISO639‑1] language code in lowercase and an ISO 3166-1 Alpha-2 [ISO3166‑1] country code in uppercase, separated by a dash. For example, en-US or fr-CA. As a compatibility note, some implementations have used an underscore as the separator rather than a dash, for example, en_US; Implementations MAY choose to accept this locale syntax as well.
     * phone_number    string    The End-User's preferred telephone number. E.164 [E.164] is RECOMMENDED as the format of this Claim. For example, +1 (425) 555-1212 or +56 (2) 687 2400.
     * address            JSON object    The End-User's preferred address. The value of the address member is a JSON [RFC4627] structure containing some or all of the members defined in Section 2.4.2.1.
     * updated_time    string    Time the End-User's information was last updated, represented as a RFC 3339 [RFC3339] datetime. For example, 2011-01-03T23:58:42+0000.
     *
     * @return mixed
     *
     */
    public function requestUserInfo($attribute = null) {

        $user_info_endpoint = $this->getProviderConfigValue("userinfo_endpoint");
        $schema = 'openid';

        $user_info_endpoint .= "?schema=" . $schema;

        //The accessToken has to be send in the Authorization header, so we create a new array with only this header.
        $headers = array("Authorization: Bearer {$this->accessToken}");

        $user_json = json_decode($this->fetchURL($user_info_endpoint,null,$headers));

        $this->userInfo = $user_json;

        if($attribute === null) {
            return $this->userInfo;
        } else if (array_key_exists($attribute, $this->userInfo)) {
            return $this->userInfo->$attribute;
        } else {
            return null;
        }
    }

    /**
     * @param $url
     * @param null $post_body string If this is set the post type will be POST
     * @param array() $headers Extra headers to be send with the request. Format as 'NameHeader: ValueHeader'
     * @throws OpenIDConnectClientException
     * @return mixed
     */
    protected function fetchURL($url, $post_body = null,$headers = array()) {


        // OK cool - then let's create a new cURL resource handle
        $ch = curl_init();

        // Determine whether this is a GET or POST
        if ($post_body != null) {
            // curl_setopt($ch, CURLOPT_POST, 1);
	    // Alows to keep the POST method even after redirect
            curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
            curl_setopt($ch, CURLOPT_POSTFIELDS, $post_body);

            // Default content type is form encoded
            $content_type = 'application/x-www-form-urlencoded';

            // Determine if this is a JSON payload and add the appropriate content type
            if (is_object(json_decode($post_body))) {
                $content_type = 'application/json';
            }

            // Add POST-specific headers
            $headers[] = "Content-Type: {$content_type}";
            $headers[] = 'Content-Length: ' . strlen($post_body);

        }

        // If we set some heaers include them
        if(count($headers) > 0) {
          curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
        }

        // Set URL to download
        curl_setopt($ch, CURLOPT_URL, $url);

        if (isset($this->httpProxy)) {
            curl_setopt($ch, CURLOPT_PROXY, $this->httpProxy);
        }

        // Include header in result? (0 = yes, 1 = no)
        curl_setopt($ch, CURLOPT_HEADER, 0);

	// Allows to follow redirect
        curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);

        /**
         * Set cert
         * Otherwise ignore SSL peer verification
         */
        if (isset($this->certPath)) {
            curl_setopt($ch, CURLOPT_CAINFO, $this->certPath);
        }

        if($this->verifyHost) {
            curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2);
        } else {
            curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
        }

        if($this->verifyPeer) {
            curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, true);
        } else {
            curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
        }

        // Should cURL return or print out the data? (true = return, false = print)
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

        // Timeout in seconds
        curl_setopt($ch, CURLOPT_TIMEOUT, $this->timeOut);

        // Download the given URL, and return output
        $output = curl_exec($ch);

        // HTTP Response code from server may be required from subclass
        $info = curl_getinfo($ch);
        $this->responseCode = $info['http_code'];

        if ($output === false) {
            throw new OpenIDConnectClientException('Curl error: ' . curl_error($ch));
        }

        // Close the cURL resource, and free system resources
        curl_close($ch);

        return $output;
    }

    /**
     * @return string
     * @throws OpenIDConnectClientException
     */
    public function getProviderURL() {

        if (!isset($this->providerConfig['issuer'])) {
            throw new OpenIDConnectClientException("The provider URL has not been set");
        } else {
            return $this->providerConfig['issuer'];
        }
    }

    /**
     * @param $url
     */
    public function redirect($url) {
        header('Location: ' . $url);
        exit;
    }

    /**
     * @param $httpProxy
     */
    public function setHttpProxy($httpProxy) {
        $this->httpProxy = $httpProxy;
    }

    /**
     * @param $certPath
     */
    public function setCertPath($certPath) {
        $this->certPath = $certPath;
    }

    /**
     * @return string|null
     */
    public function getCertPath()
    {
        return $this->certPath;
    }

    /**
     * @param bool $verifyPeer
     */
    public function setVerifyPeer($verifyPeer) {
        $this->verifyPeer = $verifyPeer;
    }

    /**
     * @param bool $verifyHost
     */
    public function setVerifyHost($verifyHost) {
        $this->verifyHost = $verifyHost;
    }

    /**
     * @return bool
     */
    public function getVerifyHost()
    {
        return $this->verifyHost;
    }

    /**
     * @return bool
     */
    public function getVerifyPeer()
    {
        return $this->verifyPeer;
    }

    /**
     *
     * Use this to alter a provider's endpoints and other attributes
     *
     * @param $array
     *        simple key => value
     */
    public function providerConfigParam($array) {
        $this->providerConfig = array_merge($this->providerConfig, $array);
    }

    /**
     * @param $clientSecret
     */
    public function setClientSecret($clientSecret) {
        $this->clientSecret = $clientSecret;
    }

    /**
     * @param $clientID
     */
    public function setClientID($clientID) {
        $this->clientID = $clientID;
    }


    /**
     * Dynamic registration
     *
     * @throws OpenIDConnectClientException
     */
    public function register() {

        $registration_endpoint = $this->getProviderConfigValue('registration_endpoint');

        $send_object = (object)array(
            'redirect_uris' => array($this->getRedirectURL()),
            'client_name' => $this->getClientName()
        );

        $response = $this->fetchURL($registration_endpoint, json_encode($send_object));

        $json_response = json_decode($response);

        // Throw some errors if we encounter them
        if ($json_response === false) {
            throw new OpenIDConnectClientException("Error registering: JSON response received from the server was invalid.");
        } elseif (isset($json_response->{'error_description'})) {
            throw new OpenIDConnectClientException($json_response->{'error_description'});
        }

        $this->setClientID($json_response->{'client_id'});

        // The OpenID Connect Dynamic registration protocol makes the client secret optional
        // and provides a registration access token and URI endpoint if it is not present
        if (isset($json_response->{'client_secret'})) {
            $this->setClientSecret($json_response->{'client_secret'});
        } else {
            throw new OpenIDConnectClientException("Error registering:
                                                    Please contact the OpenID Connect provider and obtain a Client ID and Secret directly from them");
        }

    }

    /**
     * @return mixed
     */
    public function getClientName() {
        return $this->clientName;
    }

    /**
     * @param $clientName
     */
    public function setClientName($clientName) {
        $this->clientName = $clientName;
    }

    /**
     * @return string
     */
    public function getClientID() {
        return $this->clientID;
    }

    /**
     * @return string
     */
    public function getClientSecret() {
        return $this->clientSecret;
    }

    /**
     * @return bool
     */
    public function canVerifySignatures() {
      return class_exists('\phpseclib\Crypt\RSA') || class_exists('Crypt_RSA');
    }

    /**
     * Set the access token.
     *
     * May be required for subclasses of this Client.
     *
     * @param mixed $accessToken
     *
     * @return void
     */
    public function setAccessToken($accessToken) {
        $this->accessToken = $accessToken;
    }

    /**
     * @return string
     */
    public function getAccessToken() {
        return $this->accessToken;
    }

    /**
     * @return string
     */
    public function getRefreshToken() {
        return $this->refreshToken;
    }

    /**
     * @return string
     */
    public function getIdToken() {
        return $this->idToken;
    }

    /**
     * @return array
     */
    public function getAccessTokenHeader() {
        return $this->decodeJWT($this->accessToken, 0);
    }

    /**
     * @return array
     */
    public function getAccessTokenPayload() {
        return $this->decodeJWT($this->accessToken, 1);
    }

    /**
     * @return array
     */
    public function getIdTokenHeader() {
        return $this->decodeJWT($this->idToken, 0);
    }

    /**
     * @return array
     */
    public function getIdTokenPayload() {
        return $this->decodeJWT($this->idToken, 1);
    }
    /**
     * @return array
     */
    public function getTokenResponse() {
        return $this->tokenResponse;
    }

    /**
     * Stores nonce
     *
     * @param string $nonce
     * @return string
     */
    protected function setNonce($nonce) {
        $_SESSION['openid_connect_nonce'] = $nonce;
        return $nonce;
    }

    /**
     * Get stored nonce
     *
     * @return string
     */
    protected function getNonce() {
        return $_SESSION['openid_connect_nonce'];
    }

    /**
     * Cleanup nonce
     *
     * @return void
     */
    protected function unsetNonce() {
        unset($_SESSION['openid_connect_nonce']);
    }

    /**
     * Stores $state
     *
     * @param string $state
     * @return string
     */
    protected function setState($state) {
        $_SESSION['openid_connect_state'] = $state;
        return $state;
    }

    /**
     * Get stored state
     *
     * @return string
     */
    protected function getState() {
        return $_SESSION['openid_connect_state'];
    }

    /**
     * Cleanup state
     *
     * @return void
     */
    protected function unsetState() {
        unset($_SESSION['openid_connect_state']);
    }

    /**
     * Get the response code from last action/curl request.
     *
     * @return int
     */
    public function getResponseCode()
    {
        return $this->responseCode;
    }

    /**
     * Set timeout (seconds)
     *
     * @param int $timeout
     */
    public function setTimeout($timeout)
    {
        $this->timeOut = $timeout;
    }

    public function getTimeout()
    {
        return $this->timeOut;
    }
	
    /**
     * Safely calculate length of binary string
     * @param string
     * @return int
     */
    private static function safeLength($str)
    {
        if (function_exists('mb_strlen')) {
            return mb_strlen($str, '8bit');
        }
        return strlen($str);
    }

    /**
     * Where has_equals is not available, this provides a timing-attack safe string comparison
     * @param $str1
     * @param $str2
     * @return bool
     */
    private static function hashEquals($str1, $str2)
    {
        $len1=static::safeLength($str1);
        $len2=static::safeLength($str2);

        //compare strings without any early abort...
        $len = min($len1, $len2);
        $status = 0;
        for ($i = 0; $i < $len; $i++) {
            $status |= (ord($str1[$i]) ^ ord($str2[$i]));
        }
        //if strings were different lengths, we fail
        $status |= ($len1 ^ $len2);
        return ($status === 0);
    }
}