Tag Archives: AWS

Get User Id in Lambda node.js

Hi everyone,

A quick post on where to find the user id (sub) in a lambda requested that has been authenticated with a congito authorizer.

You’ll be able to find everything you need in the event object under requestContext > authorizer > claims:

exports.viewContextHandler = async (event, context, callback) => {

"requestContext": {
    "resourceId": "XXXXX",
    "authorizer": {
        "claims": {
            "at_hash": "XXXXX",
            "sub": "XXXXX-XXXXX-XXXXX-XXXXX-XXXXX",
            "aud": "XXXXX12341234512345XXXXX",
            "email_verified": "true",
            "token_use": "id",
            "auth_time": "1547371205",
            "iss": "https://cognito-XXXXX.com/XXXXX",
            "cognito:username": "XXXXX-XXXXX-XXXXX-XXXXX-XXXXX",
            "exp": "Sun Jan 13 10:20:05 UTC 2019",
            "iat": "Sun Jan 13 09:20:05 UTC 2019",
            "email": "XXXXX@XXXXX.XXXXX"

Cognito Auth with AWS SAM

Hi everyone,

I’ve spent today implementing Cognito with AWS SAM and it took quite a while to work out what needed to be done – unfortunately there’s a lot of conflicting doco out there. Posting a sample template just in case it’s able to help anyone else out.

The first thing to do is to explicitly define you rest API. By default AWS SAM will generate one with a default logical id of ServerlessRestApi. You’ll need to override this:

  # See links for more info
  # Referencing cognito authorizer: https://github.com/awslabs/serverless-application-model/issues/512#issuecomment-411284092
  # Logical id is auto generated: https://github.com/awslabs/serverless-application-model/blob/master/docs/internals/generated_resources.rst#api
  # Sample template.yml: https://github.com/awslabs/serverless-application-model/blob/release/v1.8.0/examples/2016-10-31/api_cognito_auth/template.yaml
    Type: "AWS::Serverless::Api"
      StageName: Prod
      Auth: # We will eventually define other auth options here such as Usage Plans/Api Keys, AWS_IAM, and Resource Policies
        DefaultAuthorizer: MyCustomCognitoAuthorizer
            UserPoolArn: !GetAtt MyCustomCognitoUserPool.Arn # Can be a string, or array
            # Identity: # Optional
              # Header: ... # Optional; Default: Authorization
              # ValidationExpression: ...  # Optional; ensures the request header matches a pattern before checking in with the Authorizer endpoint; is there a default we can set for Cognito User Pools Auth?

You’ll also need to create a user pool and client:

# Creating a cognito user pool - https://github.com/awslabs/serverless-application-model/blob/master/examples/2016-10-31/api_cognito_auth/template.yaml
    Type: AWS::Cognito::UserPool
      UserPoolName: !Ref CognitoUserPoolName
      # LambdaConfig:
        # PreSignUp: !GetAtt PreSignupLambdaFunction.Arn
          MinimumLength: 8
        - email
        - AttributeDataType: String
          Name: email
          Required: false

    Type: AWS::Cognito::UserPoolClient
      UserPoolId: !Ref MyCustomCognitoUserPool
      ClientName: !Ref CognitoUserPoolClientName
      GenerateSecret: false

You then add the api id and the auth attribute to each of your function properties. If you’ve used the default authorizer property when defining the associated api you can override it by using authorizer: none.

    Type: AWS::Serverless::Function
      Handler: breed.getBreedHandler
      Policies: arn:aws:iam::aws:policy/AmazonDynamoDBFullAccess
      Runtime: nodejs8.10
          TABLE_CAT_BREED: !Ref CatBreedTable
          Type: Api
            Path: /breed/{breedId}
            Method: get
            RestApiId: !Ref MyCustomCustomApi
              Authorizer: NONE

Hopefully that’s able to help you out. If you run into any trouble I found the following link pretty useful: https://github.com/awslabs/serverless-application-model/blob/release/v1.8.0/examples/2016-10-31/api_cognito_auth/template.yaml

AWS SAM not re-creating DynamoDb Table that was manually deleted – CodeStar

Hi everyone,

I ran into a bit of an issue after deleting a DynamoDb table via the AWS Console that had been created via CloudFormation (using AWS SAM). After deleting it I had expected it to be re-created automatically on the next deploy. Unfortunately this didn’t happen.

I came across the following AWS article that does a pretty good job of summarising the issue: https://aws.amazon.com/premiumsupport/knowledge-center/failing-stack-updates-deleted/

To fix it, I removed all references to the table from my template.yml file (this includes the table definition and any !Ref tags). After pushing this changeset I returned all of the references and re-pushed.

Let me know if you have any issues!


mocha tests/* sh: 1: mocha: Permission denied – AWS CodeBuild with Node.js

Hi everyone,

I ran into the following error while running a Node.js build with AWS CodeBuild:

mocha tests/* sh: 1: mocha: Permission denied

To resolve this I removed node_modules from my repository and added it to .gitignore:


Thanks to the following links for the info:
Add node_modules to gitignore: https://stackoverflow.com/a/29820869/522859
Misc background issues: https://github.com/mochajs/mocha/issues/1487

Parsing DynamoDB Items – AWS Lambda with Node.js

Hi everyone,

A quick post on how to parse DynamoDB items into something more readable when using lambda with Node.js:



    CatBreedId: { S: '17acbc81-2b4a-462b-be87-bcc49580b1ae'},
    Name: { S: 'Cat #1'}



    "CatBreedId": "17acbc81-2b4a-462b-be87-bcc49580b1ae",
    "Name": "Cat #1"

Official doco is here: https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/DynamoDB/Converter.html

Thanks to the following stackoverflow post for the info: https://stackoverflow.com/a/44536616/522859

Create DynamoDB Table – AWS CLI

Hi everyone,

A quick example of how to create a dynamodb table using the AWS CLI:

aws dynamodb create-table --table-name CatBreeds --attribute-definitions AttributeName=CatBreedId,AttributeType=S --key-schema AttributeName=CatBreedId,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

For more info the following AWS page helped me: https://docs.aws.amazon.com/cli/latest/reference/dynamodb/create-table.html

AWS IoT – error in discovery certificate_verify_failed

Hi everyone,

I ran into the following error while using the AWS IoT python SDK:

Error in discovery!
Error message: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:720)

It turns out that this was because I was using the wrong root certificate. In the documentation there are five certificates listed:

  • RSA 2048 bit key: VeriSign Class 3 Public Primary G5 root CA certificate
  • RSA 2048 bit key: Amazon Root CA 1
  • RSA 4096 bit key: Amazon Root CA 2
  • ECC 256 bit key: Amazon Root CA 3
  • ECC 384 bit key: Amazon Root CA 4

If you’re using the console to create the certificate and have already downloaded your device cert, public cert and private key you can use Amazon Root CA 1: https://www.amazontrust.com/repository/AmazonRootCA1.pem

As soon as that was added the error was resolved and I was able to move onto the next one. I found most of the info on the AWS forums but let me know if you have any questions: https://forums.aws.amazon.com/thread.jspa?threadID=286871

AWS 2_ContinuousDeliveryPipeline Tutorial – Error: no test specified

Hi everyone,

I ran into the following error while completing an AWS tutorial: https://github.com/aws-samples/aws-serverless-workshops/tree/master/DevOps/2_ContinuousDeliveryPipeline

C:UsersChris-PCsourcereposUniApiuni-apitest>npm test

> uni-api-test@1.0.0 test C:UsersChris-PCsourcereposUniApiuni-api
> echo ‘Error: no test specified’

‘Error: no test specified’

The solution was to add the following line to my package.json file:

“scripts”: {“test”: “mocha”}

Now when running npm test I get the expected test output:

4 passing (24ms)
1 failing

1) Reading Unicorns
errors on missing unicorn data:

AssertionError [ERR_ASSERTION]: 500 == 404
+ expected – actual


at lambda.lambda_handler (testread.spec.js:77:20)
at appread.js:20:10
at Object.get (testread.spec.js:34:33)
at Object.exports.lambda_handler (appread.js:18:13)
at Context. (testread.spec.js:65:16)

npm ERR! Test failed. See above for more details.

Thanks to this link for the answer: https://teamtreehouse.com/community/when-i-run-test-i-am-getting-an-error-that-says-no-test-specified

Parsing Hash Args for Cognito Auth – Javascript

Hi everyone,

A quick post on a function for parsing hash args when using AWS Congito.


Just in case the fiddle ever disappears:

const parseHashArgs = aURL => {

  aURL = aURL || window.location.href;

  var vars = {};
  var hashes = aURL.slice(aURL.indexOf('#') + 1).split('&');

  for (var i = 0; i  1) {
      vars[hash[0]] = hash[1];
    } else {
      vars[hash[0]] = null;

  return vars;


Thanks to this link on Github: https://gist.github.com/miohtama/1570295/289d5a82e65663c9b515c88186a268c6dd1fddb7