config.default.js

exports.oss = {
  client: {
    async clientLoadConfig(config, app) {
      assert(app && app.name === 'oss-async-load');
      return Object.assign({ something: 'individual' }, config);
    },
  },
  default: {
    async loadConfig(config, app) {
      assert(app && app.name === 'oss-async-load');
      return Object.assign({}, { something: 'basic' }, config);
    },
  },

lib-oss.js

// line 17
app.addSingleton('oss', async (config, app) => {
  config = Object.assign({}, config, { urllib: app.httpclient });
  if (is.function(config.loadConfig)) {
    const result = config.loadConfig(config, app);
    config = Object.assign({}, is.promise(result) ? (await result) : result, config);
    delete config.loadConfig;
  }
  if (is.function(config.clientLoadConfig)) {
    const result = config.clientLoadConfig(config, app);
    config = Object.assign({}, is.promise(result) ? (await result) : result, config);
    delete config.clientLoadConfig;
  }
  // the rest
}