@Override
    public void setup(final Map<String,Object> config) {
        logger.info("Initializing authentication with the {}", SimpleAuthenticator.class.getName());

        if (null == config) {
            throw new IllegalArgumentException(String.format(
                    "Could not configure a %s - provide a 'config' in the 'authentication' settings",
                    SimpleAuthenticator.class.getName()));
        }

        if (!config.containsKey(CONFIG_CREDENTIALS_DB)) {
            throw new IllegalStateException(String.format(
                    "Credentials configuration missing the %s key that points to a graph config file", CONFIG_CREDENTIALS_DB));
        }

        final Graph graph = GraphFactory.open((String) config.get(CONFIG_CREDENTIALS_DB));

        if (graph instanceof TinkerGraph) {
            // have to create the indices because they are not stored in gryo
            final TinkerGraph tinkerGraph = (TinkerGraph) graph;
            tinkerGraph.createIndex(PROPERTY_USERNAME, Vertex.class);
        }

        credentialStore = graph.traversal(CredentialTraversalSource.class);
        logger.info("CredentialGraph initialized at {}", credentialStore);
    }
The location of the configuration file that contains the credentials database.
gremlin-server/src/main/java/org/apache/tinkerpop/gremlin/server/auth/SimpleAuthenticator.java