def repo_exists(self, auth, username, repo_name):
        """
        Returns whether a repository with name ``repo_name`` owned by the user with username ``username`` exists.

        :param auth.Authentication auth: authentication object
        :param str username: username of owner of repository
        :param str repo_name: name of repository
        :return: whether the repository exists
        :rtype: bool
        :raises NetworkFailure: if there is an error communicating with the server
        :raises ApiFailure: if the request cannot be serviced
        """
        path = "/repos/{u}/{r}".format(u=username, r=repo_name)
        return self._get(path, auth=auth).ok