How to debug creating Cognito PostConfirmation trigger with SAM

Question

I'm not able to understand why my Cognito trigger is not firing my Lambda function. Can anyone suggest either what is wrong, or point me at a way of finding why it's not working.

I am able to trigger the function manually from the AWS console - I'm verifying this by looking at the generated log files in the console.

My SAM template looks like this:

  UserPool:
    Type: AWS::Cognito::UserPool
    Properties:
      AdminCreateUserConfig:
        AllowAdminCreateUserOnly: false
      UsernameAttributes:
        - email
      AutoVerifiedAttributes:
        - email
      Policies:
        PasswordPolicy:
          MinimumLength: 8
          RequireLowercase: true
          RequireNumbers: false
          RequireSymbols: false
          RequireUppercase: true
          TemporaryPasswordValidityDays: 90
      LambdaConfig:
        PostConfirmation: !GetAtt ConfirmUserFunction.Arn

  UserPoolInvokeConfirmUserFunctionPermission:
    Type: AWS::Lambda::Permission
    Properties:
      Action: lambda:InvokeFunction
      FunctionName: !GetAtt ConfirmUserFunction.Arn
      Principal: cognito-idp.amazonaws.com
      SourceArn: !GetAtt UserPool.Arn

  ConfirmUserFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: lambdas/ConfirmUser
      Handler: app.lambda_handler
      Runtime: python3.8
      MemorySize: 128
      Timeout: 10

Have I missed something obvious?

I have also tried setting the event trigger on the lambda function, using:

      Events:
        CognitoUserPoolConfirmed:
          Type: Cognito
          Properties:
            UserPool:
              Ref: UserPool
            Trigger: PostConfirmation

This doesn't seem to make any difference at all.

I am able to successfully setup a trigger from a PostAuthentication trigger to the same Lambda, so my template can't be too far off, but I still can't see what the issue is.

score 3 · Answer 1 · answered Jan 24 '21 at 20:52

@Richard,

please try the sam definition below.

userAutoConfirmFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: src/auth/autoConfirm.handler
      Runtime: nodejs12.x
      Timeout: 10
      Description: Function to autoConfirm user.
      Events:
        CognitoEvent:
          Type: Cognito
          Properties:
            UserPool: !Ref UserPool
            Trigger: PreSignUp

UserPool:
    Type: AWS::Cognito::UserPool
    Properties:
      AdminCreateUserConfig:
        AllowAdminCreateUserOnly: false
      UserPoolName: ausavaUsers
      UsernameAttributes:
      - email
      AutoVerifiedAttributes:
      - email
      Policies:
        PasswordPolicy:
          MinimumLength: 6
          RequireLowercase: true
          RequireNumbers: false
          RequireSymbols: false
          RequireUppercase: true

This template worked for me.

How to debug creating Cognito PostConfirmation trigger with SAM

1 Answers1