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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _do_server_auth(conn, auth_secret):
 """ Performs the authentication protocol defined by the SocketAuthHelper class on the given file-like object 'conn'. """

    write_with_length(auth_secret.encode("utf-8"), conn)
    conn.flush()
    reply = UTF8Deserializer().loads(conn)
    if reply != "ok":
        conn.close()
        raise Exception("Unexpected reply from iterator server.")