public static function verify_user($oauth_token, $github_username) {
	$known_login = static::get_by_oauth_token($oauth_token);
	if (empty($known_login)) {
		return true;
	}
	
	if ($known_login->github_username != $github_username) {
		$exception = bootstrap::get_library('exception');
		throw new $exception('oauth token switched user');
	}
	
	return true;
}