JWT refresh tokens not required for re-authentication - oauth-2.0

Question

Till now i am using short-lived token and refresh token for API auth. I am using refresh token only for getting user-id to query database to check latest permissions and active/blocked status of user. Now i am thinking that why should not i extract this user-id from short-liven token itself. The following function is used to decode JWT, in this expiration is verified after signature verification. So if i get 'expiration' error it means then token signature is good and token is un-tempered. Now i can extract middle(yyy out of xxx.yyy.zzz) base64 encoded data from expired JWT to get user-id. So i don't seeing worth using refresh token. Further longer time access can also be defined in token itself with just custom timestamp so that i have both time limits in one token for example 5 minutes and 90 days. What are your thoughts?
public static function decode($jwt, $key, array $allowed_algs = array())
{
$timestamp = is_null(static::$timestamp) ? time() : static::$timestamp;
if (empty($key)) {
throw new InvalidArgumentException('Key may not be empty');
}
$tks = explode('.', $jwt);
if (count($tks) != 3) {
throw new UnexpectedValueException('Wrong number of segments');
}
list($headb64, $bodyb64, $cryptob64) = $tks;
if (null === ($header = static::jsonDecode(static::urlsafeB64Decode($headb64)))) {
throw new UnexpectedValueException('Invalid header encoding');
}
if (null === $payload = static::jsonDecode(static::urlsafeB64Decode($bodyb64))) {
throw new UnexpectedValueException('Invalid claims encoding');
}
if (false === ($sig = static::urlsafeB64Decode($cryptob64))) {
throw new UnexpectedValueException('Invalid signature encoding');
}
if (empty($header->alg)) {
throw new UnexpectedValueException('Empty algorithm');
}
if (empty(static::$supported_algs[$header->alg])) {
throw new UnexpectedValueException('Algorithm not supported');
}
if (!in_array($header->alg, $allowed_algs)) {
throw new UnexpectedValueException('Algorithm not allowed');
}
if (is_array($key) || $key instanceof \ArrayAccess) {
if (isset($header->kid)) {
if (!isset($key[$header->kid])) {
throw new UnexpectedValueException('"kid" invalid, unable to lookup correct key');
}
$key = $key[$header->kid];
} else {
throw new UnexpectedValueException('"kid" empty, unable to lookup correct key');
}
}
// Check the signature
if (!static::verify("$headb64.$bodyb64", $sig, $key, $header->alg)) {
throw new SignatureInvalidException('Signature verification failed');
}
// Check the nbf if it is defined. This is the time that the
// token can actually be used. If it's not yet that time, abort.
if (isset($payload->nbf) && $payload->nbf > ($timestamp + static::$leeway)) {
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) && $payload->iat > ($timestamp + static::$leeway)) {
throw new BeforeValidException(
'Cannot handle token prior to ' . date(DateTime::ISO8601, $payload->iat)
);
}
// Check if this token has expired.
if (isset($payload->exp) && ($timestamp - static::$leeway) >= $payload->exp) {
throw new ExpiredException('Expired token');
}
return $payload;
}

Answer 1

Don't do this. Your plan breaks the common practice. It is also against the OAuth standard. New developer will think it is a bug. Your company might hire security auditor and that person will test access with expired token. This will be reported as something you have to fix.