function _openid_hmac($key, $text) {
if (strlen($key) > OPENID_SHA1_BLOCKSIZE) {
$key = sha1($key, TRUE);
}
$key = str_pad($key, OPENID_SHA1_BLOCKSIZE, chr(0x0));
$ipad = str_repeat(chr(0x36), OPENID_SHA1_BLOCKSIZE);
$opad = str_repeat(chr(0x5c), OPENID_SHA1_BLOCKSIZE);
$hash1 = sha1(($key ^ $ipad) . $text, TRUE);
$hmac = sha1(($key ^ $opad) . $hash1, TRUE);
return $hmac;
}