Get AWS Cognito user ID in Serverless Java function

Question

I am following the https://serverless-stack.com/ tutorial which uses the Serverless framework to create an API that inserts objects into a DynamoDB table and associates them to the authenticated AWS Cognito user. I am attempting to convert the Node.js code to Java but I have hit a problem when getting the Cognito identity as shown on this page

userId: event.requestContext.identity.cognitoIdentityId,

I expected the following lines of Java code to be equivalent:

final CognitoIdentity identity = context.getIdentity();
final String userId = identity.getIdentityId();

but userId is empty.

I am using the aws-api-gateway-cli-test utility to call my API with credentials of a Cognito user as shown on this page. The authentication passes but the userId is empty in the handler.

This is my function:

package com.mealplanner.function;

import java.util.Map;

import com.amazonaws.services.lambda.runtime.CognitoIdentity;
import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestHandler;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.mealplanner.dal.MealRepository;
import com.mealplanner.domain.Meal;
import com.serverless.ApiGatewayResponse;

public class CreateMealHandler implements RequestHandler<Map<String, Object>, ApiGatewayResponse> {

    @Override
    public ApiGatewayResponse handleRequest(final Map<String, Object> request, final Context context) {
        try {
            final CognitoIdentity identity = context.getIdentity();    
            final String userId = identity.getIdentityId();

            final JsonNode body = new ObjectMapper().readTree((String) request.get("body"));
            final MealRepository repository = new MealRepository();
            final Meal meal = new Meal();
            meal.setUserId(userId);
            meal.setDescription(body.get("description").asText());
            repository.save(meal);

            return ApiGatewayResponse.builder()
                    .setStatusCode(200)
                    .setObjectBody(meal)
                    .build();
        } catch (final Exception e) {
            final String errorText = String.format("Error saving meal with request [%s]", request);
            LOGGER.error(errorText, e);
            return ApiGatewayResponse.builder()
                    .setStatusCode(500)
                    .setObjectBody(errorText)
                    .build();
        }
    }
}

And this is the function definition in serverless.yml:

createMeal:
    handler: com.mealplanner.function.CreateMealHandler
    events:
      - http:
          path: /meals
          method: post
          cors: true
          authorizer: aws_iam

Am I missing some configuration or have I not translated the Node.js code correctly?

In case I have missed any pertinent information the full code is available here: https://github.com/stuartleylandcole/meal-planner/tree/add-users. I will update this question with anything that is missing to ensure all relevant information is self-contained.

Stuart Leyland-Cole Stuart Leyland-Cole · Accepted Answer · 2018-07-20T11:01:08

It turns out I hadn't translated the Node.js code correctly. To access the CognitoIdentityId I had to get the requestContext from the request object, then get the identity object, like so:

public ApiGatewayResponse handleRequest(final Map<String, Object> request, final Context context) {
    final Map<String, Object> requestContext = (Map<String, Object>) request.get("requestContext");
    final Map<String, Object> identity = (Map<String, Object>) requestContext.get("identity");
    final String userId = (String) identity.get("cognitoIdentityId");

    // etc
}

Get AWS Cognito user ID in Serverless Java function

1 Answers