async def user_exists(app, **kwargs):
    """Check if a user exists by arbitrary keys.

    Parameters
    ----------
    app : aiohttp.web.Application
        The aiohttp application instance
    **kwargs : dict
        The properties and values to be seached for
    Returns
    -------
    exists : bool
        True if the user exists, False otherwise
    """
    return app["db"].users.count_documents(kwargs) > 0