code: function getCacheKey(request) {
    var service = request.service;
    var api = service.api || {};
    var operations = api.operations;
    var identifiers = {};
    if (service.config.region) {
      identifiers.region = service.config.region;
    }
    if (api.serviceId) {
      identifiers.serviceId = api.serviceId;
    }
    if (service.config.credentials.accessKeyId) {
      identifiers.accessKeyId = service.config.credentials.accessKeyId;
    }
    return identifiers;
  }
docs: Generate key (except resources and operation part) to index the endpoints in the cache
  If input shape has endpointdiscoveryid trait then use
  accessKey + operation + resources + region + service as cache key
  If input shape doesn't have endpointdiscoveryid trait then use
  accessKey + region + service as cache key
  @return [map<String,String>] object with keys to index endpoints.
  @api private