@Override
public Account verify(String id, Credential credential) {
    if (id == null || id.length() == 0) {
        HttpServerLogger.ROOT_LOGGER.debug("Missing or empty username received, aborting account verification.");
        return null;
    }

    if (credential instanceof PasswordCredential) {
        return verify(id, (PasswordCredential) credential);
    } else if (credential instanceof DigestCredential) {
        return verify(id, (DigestCredential) credential);
    }

    throw HttpServerLogger.ROOT_LOGGER.invalidCredentialType(credential.getClass().getName());
}