private function makeSignedJwt($payload)
{
$header = array("typ" => "JWT", "alg" => "RS256");
$segments = array();
$segments[] = apiOAuth2::urlSafeB64Encode(json_encode($header));
$segments[] = apiOAuth2::urlSafeB64Encode(json_encode($payload));
$signing_input = implode(".", $segments);
$signature = $this->signer->sign($signing_input);
$segments[] = apiOAuth2::urlSafeB64Encode($signature);
return implode(".", $segments);
}