A connection must use one of the supported authorization types
        to prove their identity. If a requester deviates
        from the procedure in any way, the requester will be rejected and the
        connection will be closed. The same is true if the requester sends
        multiple ConnectionRequests or multiple of any authorization-type
        message. The validator receiving a new connection will receive a
        ConnectionRequest. The validator will respond with a ConnectionResponse
        message. The ConnectionResponse message will contain a list of
        RoleEntry messages and an AuthorizationType. Role entries are
        the accepted type of connections that are supported on the endpoint
        that the ConnectionRequest was sent to. AuthorizationType describes the
        procedure required to gain access to that role. If the validator is not
        accepting connections or does not support the listed authorization
        type, return an ConnectionResponse.ERROR and close the connection.

def handle(self, connection_id, message_content):
        """
        A connection must use one of the supported authorization types
        to prove their identity. If a requester deviates
        from the procedure in any way, the requester will be rejected and the
        connection will be closed. The same is true if the requester sends
        multiple ConnectionRequests or multiple of any authorization-type
        message. The validator receiving a new connection will receive a
        ConnectionRequest. The validator will respond with a ConnectionResponse
        message. The ConnectionResponse message will contain a list of
        RoleEntry messages and an AuthorizationType. Role entries are
        the accepted type of connections that are supported on the endpoint
        that the ConnectionRequest was sent to. AuthorizationType describes the
        procedure required to gain access to that role. If the validator is not
        accepting connections or does not support the listed authorization
        type, return an ConnectionResponse.ERROR and close the connection.
        """
        message = ConnectionRequest()
        message.ParseFromString(message_content)
        LOGGER.debug("got connect message from %s. sending ack", connection_id)

        # Need to use join here to get the string "0.0.0.0". Otherwise,
        # bandit thinks we are binding to all interfaces and returns a
        # Medium security risk.
        interfaces = ["*", ".".join(["0", "0", "0", "0"])]
        interfaces += netifaces.interfaces()
        if self.is_valid_endpoint_host(interfaces, message.endpoint) is False:
            LOGGER.warning("Connecting peer provided an invalid endpoint: %s; "
                           "Ignoring connection request.",
                           message.endpoint)
            connection_response = ConnectionResponse(
                status=ConnectionResponse.ERROR)
            return HandlerResult(
                HandlerStatus.RETURN_AND_CLOSE,
                message_out=connection_response,
                message_type=validator_pb2.Message.
                AUTHORIZATION_CONNECTION_RESPONSE)

        LOGGER.debug("Endpoint of connecting node is %s", message.endpoint)
        self._network.update_connection_endpoint(connection_id,
                                                 message.endpoint)

        # Get what AuthorizationType the network role requires
        roles = self._network.roles
        auth_type = roles.get("network")
        if auth_type == AuthorizationType.TRUST:
            role_type = ConnectionResponse.RoleEntry(
                role=RoleType.Value("NETWORK"),
                auth_type=ConnectionResponse.TRUST)
            connection_response = ConnectionResponse(roles=[role_type])
        elif auth_type == AuthorizationType.CHALLENGE:
            role_type = ConnectionResponse.RoleEntry(
                role=RoleType.Value("NETWORK"),
                auth_type=ConnectionResponse.CHALLENGE)
            connection_response = ConnectionResponse(roles=[role_type])
        else:
            LOGGER.warning("Network role is set to an unsupported"
                           "Authorization Type: %s", auth_type)
            connection_response = ConnectionResponse(
                status=ConnectionResponse.ERROR)
            return HandlerResult(
                HandlerStatus.RETURN_AND_CLOSE,
                message_out=connection_response,
                message_type=validator_pb2.Message.
                AUTHORIZATION_CONNECTION_RESPONSE)

        try:
            is_outbound_connection = self._network.is_outbound_connection(
                connection_id)
        except KeyError:
            # Connection has gone away, drop message
            return HandlerResult(HandlerStatus.DROP)

        if not is_outbound_connection:
            if self._network.allow_inbound_connection():
                LOGGER.debug("Allowing incoming connection: %s", connection_id)
                connection_response.status = connection_response.OK
            else:
                connection_response.status = connection_response.ERROR
                return HandlerResult(
                    HandlerStatus.RETURN_AND_CLOSE,
                    message_out=connection_response,
                    message_type=validator_pb2.Message.
                    AUTHORIZATION_CONNECTION_RESPONSE)

        if self._network.get_connection_status(connection_id) is not None:
            LOGGER.debug("Connection has already sent ConnectionRequest:"
                         " %s, Remove connection.", connection_id)
            connection_response.status = connection_response.ERROR
            return HandlerResult(
                HandlerStatus.RETURN_AND_CLOSE,
                message_out=connection_response,
                message_type=validator_pb2.Message.
                AUTHORIZATION_CONNECTION_RESPONSE)

        self._network.update_connection_status(
            connection_id,
            ConnectionStatus.CONNECTION_REQUEST)

        return HandlerResult(
            HandlerStatus.RETURN,
            message_out=connection_response,
            message_type=validator_pb2.Message.
            AUTHORIZATION_CONNECTION_RESPONSE)