def _token_str(
        *,
        token_type: str,
        token_version: str,
        data: str,
) -> str:
    """Returns a token string.

    Args:
        token_type: What this token is for.
        token_version: Version of this token. If the token string changes for
            the same entity, this should change too.
        data: Contents of the token.
    """
    return f'{token_type}/{token_version}:{data}'