function verify($assoc_handle, $sig, $signed_pairs)
    {
        $assoc = $this->getAssociation($assoc_handle, true);
        if (!$assoc) {
            // oidutil.log("failed to get assoc with handle %r to verify sig %r"
            //             % (assoc_handle, sig))
            return false;
        }

        $expected_sig = base64_encode($assoc->sign($signed_pairs));

        return $sig == $expected_sig;
    }

    /**
     * Given a response, sign the fields in the response's 'signed'
     * list, and insert the signature into the response.
     */
    function sign($response)
    {
        $signed_response = $response;
        $assoc_handle = $response->request->assoc_handle;

        if ($assoc_handle) {
            // normal mode
            $assoc = $this->getAssociation($assoc_handle, false);
            if (!$assoc) {
                // fall back to dumb mode
                $signed_response->fields['invalidate_handle'] = $assoc_handle;
                $assoc = $this->createAssociation(true);
            }
        } else {
            // dumb mode.
            $assoc = $this->createAssociation(true);
        }

        $signed_response->fields['assoc_handle'] = $assoc->handle;
        $assoc->addSignature($signed_response->signed,
                             $signed_response->fields, '');
        return $signed_response;
    }

    /**
     * Make a new association.
     */
    function createAssociation($dumb = true, $assoc_type = 'HMAC-SHA1')
    {
        $secret = Auth_OpenID_CryptUtil::getBytes(20);
        $uniq = base64_encode(Auth_OpenID_CryptUtil::getBytes(4));
        $handle = sprintf('{%s}{%x}{%s}', $assoc_type, intval(time()), $uniq);

        $assoc = Auth_OpenID_Association::fromExpiresIn(
                      $this->SECRET_LIFETIME, $handle, $secret, $assoc_type);

        if ($dumb) {
            $key = $this->dumb_key;
        } else {
            $key = $this->normal_key;
        }

        $this->store->storeAssociation($key, $assoc);
        return $assoc;
    }

    /**
     * Given an association handle, get the association from the
     * store, or return a ServerError or null if something goes wrong.
     */
    function getAssociation($assoc_handle, $dumb)
    {
        if ($assoc_handle === null) {
            return new Auth_OpenID_ServerError(null,
                                     "assoc_handle must not be null");
        }

        if ($dumb) {
            $key = $this->dumb_key;
        } else {
            $key = $this->normal_key;
        }

        $assoc = $this->store->getAssociation($key, $assoc_handle);

        if (($assoc !== null) && ($assoc->getExpiresIn() <= 0)) {
            $this->store->removeAssociation($key, $assoc_handle);
            $assoc = null;
        }

        return $assoc;
    }

    /**
     * Invalidate a given association handle.
     */
    function invalidate($assoc_handle, $dumb)
    {
        if ($dumb) {
            $key = $this->dumb_key;
        } else {
            $key = $this->normal_key;
        }
        $this->store->removeAssociation($key, $assoc_handle);
    }
}

/**
 * Encode an Auth_OpenID_Response to an Auth_OpenID_WebResponse.
 *
 * @package OpenID
 */
class Auth_OpenID_Encoder {

    var $responseFactory = 'Auth_OpenID_WebResponse';

    /**
     * Encode an Auth_OpenID_Response and return an
     * Auth_OpenID_WebResponse.
     */
    function encode(&$response)
    {
        global $_Auth_OpenID_Encode_Kvform,
            $_Auth_OpenID_Encode_Url;

        $cls = $this->responseFactory;

        $encode_as = $response->whichEncoding();
        if ($encode_as == $_Auth_OpenID_Encode_Kvform) {
            $wr = new $cls(null, null, $response->encodeToKVForm());
            if (is_a($response, 'Auth_OpenID_ServerError')) {
                $wr->code = AUTH_OPENID_HTTP_ERROR;
            }
        } else if ($encode_as == $_Auth_OpenID_Encode_Url) {
            $location = $response->encodeToURL();
            $wr = new $cls(AUTH_OPENID_HTTP_REDIRECT,
                           array('location' => $location));
        } else {
            return new Auth_OpenID_EncodingError($response);
        }
        return $wr;
    }
}

/**
 * Returns true if the given response needs a signature.
 *
 * @access private
 */
function needsSigning($response)
{
    return (in_array($response->request->mode, array('checkid_setup',
                                                     'checkid_immediate')) &&
            $response->signed);
}

/**
 * An encoder which also takes care of signing fields when required.
 *
 * @package OpenID
 */
class Auth_OpenID_SigningEncoder extends Auth_OpenID_Encoder {

    function Auth_OpenID_SigningEncoder(&$signatory)
    {
        $this->signatory =& $signatory;
    }

    /**
     * Sign an Auth_OpenID_Response and return an
     * Auth_OpenID_WebResponse.
     */
    function encode(&$response)
    {
        // the isinstance is a bit of a kludge... it means there isn't
        // really an adapter to make the interfaces quite match.
        if (!is_a($response, 'Auth_OpenID_ServerError') &&
            needsSigning($response)) {

            if (!$this->signatory) {
                return new Auth_OpenID_ServerError(null,
                                       "Must have a store to sign request");
            }
            if (array_key_exists('sig', $response->fields)) {
                return new Auth_OpenID_AlreadySigned($response);
            }
            $response = $this->signatory->sign($response);
        }
        return parent::encode($response);
    }
}

/**
 * Decode an incoming Auth_OpenID_WebResponse into an
 * Auth_OpenID_Request.
 *
 * @package OpenID
 */
class Auth_OpenID_Decoder {

    function Auth_OpenID_Decoder()
    {
        global $_Auth_OpenID_OpenID_Prefix;
        $this->prefix = $_Auth_OpenID_OpenID_Prefix;

        $this->handlers = array(
            'checkid_setup' => 'Auth_OpenID_CheckIDRequest',
            'checkid_immediate' => 'Auth_OpenID_CheckIDRequest',
            'check_authentication' => 'Auth_OpenID_CheckAuthRequest',
            'associate' => 'Auth_OpenID_AssociateRequest'
            );
    }

    /**
     * Given an HTTP query in an array (key-value pairs), decode it
     * into an Auth_OpenID_Request object.
     */
    function decode($query)
    {
        if (!$query) {
            return null;
        }

        $myquery = array();

        foreach ($query as $k => $v) {
            if (strpos($k, $this->prefix) === 0) {
                $myquery[$k] = $v;
            }
        }

        if (!$myquery) {
            return null;
        }

        $mode = Auth_OpenID::arrayGet($myquery, $this->prefix . 'mode');
        if (!$mode) {
            return new Auth_OpenID_ServerError($query,
                           sprintf("No %s mode found in query", $this->prefix));
        }

        $handlerCls = Auth_OpenID::arrayGet($this->handlers, $mode,
                                            $this->defaultDecoder($query));

        if (!is_a($handlerCls, 'Auth_OpenID_ServerError')) {
            return call_user_func_array(array($handlerCls, 'fromQuery'),
                                        array($query));
        } else {
            return $handlerCls;
        }
    }

    fun