ProviderARNs need to be valid Cognito Userpools

Question

I'm trying to use a list of string inside a sam template but it doesn't work as expected. There is my code

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: >
  Sample SAM Template

Parameters:
  CognitoPoolArns:
    Type: List<String>
    Default: "[\"arn:aws:cognito-idp:eu-west-X:XXXXX:userpool/eu-west-XXXXXXX\",\"arn:aws:cognito-idp:eu-west-X:XXXXXX:userpool/eu-west-XXXXXX\",]"
  

Resources:
 Api:
    Type: AWS::Serverless::Api
    Properties:
      StageName: dev
      Name: name
      EndpointConfiguration:
        Type: REGIONAL
      Auth:
        DefaultAuthorizer: MyCognitoAuthorizer
        Authorizers:
          MyCognitoAuthorizer:
            UserPoolArn: !Ref CognitoPoolArns
        

  PingGetFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: lambdas/ping_get/
      FunctionName: get-ping
      Handler: main.lambda_handler
      Runtime: python3.8
      Events:
        API:
          Type: Api
          Properties:
            RestApiId: !Ref Api
            Path: /api/v1/ping
            Method: get

I get this error message : Errors found during import: Unable to create authorizer 'MyCognitoAuthorizer': ProviderARNs need to be valid Cognito Userpools. Invalid ARNs- ["arn:aws:cognito-idp:eu- west-X:XXXX:userpool/eu- west-XXXXX" "arn:aws:cognito-idp:eu- west-X:XXXXXX:userpool/eu- west-XXXXX" ]

But if I do

MyCognitoAuthorizer:
                UserPoolArn: 
                       - arn:aws:cognito-idp:eu-west-X:XXX:userpool/eu-west-XXXXXXXX
                       - arn:aws:cognito-idp:eu-west-X:XXX:userpool/eu-west-XXXXXXXX

It's working. How can I deal with that by passing by variable ?

Answer 1

Change the default value of CognitoPoolArns parameter in the template as below to resolve the error.

Execute sam build command after making the change and then you will be able to deploy successfully.

Default: "arn:aws:cognito-idp:eu-west-X:XXXXX:userpool/eu-west-XXXXXXX, arn:aws:cognito-idp:eu-west-X:XXXXXX:userpool/eu-west-XXXXXX"