public static void updateComponentSecret(String subdomain, String secret) throws ModificationNotAllowedException {
        // Alert listeners about this event
        for (ExternalComponentManagerListener listener : listeners) {
            try {
                listener.componentSecretUpdated(subdomain, secret);
            } catch (Exception e) {
                Log.warn("An exception occurred while dispatching a 'componentSecretUpdated' event!", e);
            }
        }
        ExternalComponentConfiguration configuration = getConfiguration(subdomain, false);
        if (configuration != null) {
            configuration.setPermission(Permission.allowed);
            configuration.setSecret(secret);
            // Remove any previous configuration for this external component
            deleteConfigurationFromDB(configuration);
        }
        else {
            configuration = new ExternalComponentConfiguration(subdomain, false, Permission.allowed, secret);
        }
        addConfiguration(configuration);
    }
Returns the list of external components that are NOT allowed to connect to this
server.

@return the configuration of the blocked external components.
xmppserver/src/main/java/org/jivesoftware/openfire/component/ExternalComponentManager.java