Работает
private SimpleMongoClientDatabaseFactory getMongoDbFactory(MongoProperties properties) throws Exception {
        MongoCredential credentials = MongoCredential.createCredential(properties.getUsername(),
                properties.getAuthenticationDatabase(), properties.getPassword());
        MongoClientSettings.Builder settings = MongoClientSettings.builder();
        settings.credential(credentials);
        StringBuilder connectionString = new StringBuilder(String.format("mongodb://%s:%d", properties.getHost(), properties.getPort()));
        ConnectionString uri = new ConnectionString(connectionString.toString());
        settings.applyConnectionString(uri);
        return new SimpleMongoClientDatabaseFactory(MongoClients.create(settings.build()), properties.getDatabase());
    }

Не работает

private SimpleMongoClientDatabaseFactory getMongoDbFactory(MongoProperties mongoProperties) throws Exception {
        MongoCredential mongoCredential = MongoCredential.createCredential(mongoProperties.getUsername(),
                mongoProperties.getAuthenticationDatabase(), mongoProperties.getPassword());
        MongoClientFactoryBean factoryBean = new MongoClientFactoryBean();
        factoryBean.setHost(mongoProperties.getHost());
        factoryBean.setPort(mongoProperties.getPort());
        factoryBean.setCredential(new MongoCredential[] {mongoCredential});
        MongoClient mongoClient = factoryBean.getObject();
        return new SimpleMongoClientDatabaseFactory(mongoClient, mongoProperties.getDatabase());
    }