public AuthenticatedUser authenticate(final Map<String, String> credentials) throws AuthenticationException {
        logger.error("Authenticate() should not be called. Use getAuthenticatedUser() when isComplete() is true.");
        return null;
    }
Called once on server startup with the authentication.config from the *.yaml file
gremlin-server/src/main/java/org/apache/tinkerpop/gremlin/server/auth/Krb5Authenticator.java