code: @Override
      public AddCustomAttributesResult addCustomAttributes(AddCustomAttributesRequest request) {
          request = beforeClientExecution(request);
          return executeAddCustomAttributes(request);
      }
docs: <p>
  Adds additional user attributes to the user pool schema.
  </p>
  
  @param addCustomAttributesRequest
  Represents the request to add custom attributes.
  @return Result of the AddCustomAttributes operation returned by the service.
  @throws ResourceNotFoundException
  This exception is thrown when the Amazon Cognito service cannot find the requested resource.
  @throws InvalidParameterException
  This exception is thrown when the Amazon Cognito service encounters an invalid parameter.
  @throws TooManyRequestsException
  This exception is thrown when the user has made too many requests for a given operation.
  @throws NotAuthorizedException
  This exception is thrown when a user is not authorized.
  @throws UserImportInProgressException
  This exception is thrown when you are trying to modify a user pool while a user import job is in progress
  for that pool.
  @throws InternalErrorException
  This exception is thrown when Amazon Cognito encounters an internal error.
  @sample AWSCognitoIdentityProvider.AddCustomAttributes
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/cognito-idp-2016-04-18/AddCustomAttributes"
  target="_top">AWS API Documentation</a>