This is a (Bug Report / Feature Proposal)

I am using a DescribeExecution aws step function integration for api gateway. I cannot update custom mapping template for 400 status if the body of the request contains non existing arn.

I am sending: POST /endpoint/path with body {"executionArn": "abcdef}. When bad request is returned I am getting:

{
  "__type": "com.amazonaws.swf.service.v2.model#InvalidArn",
  "message": "Invalid Arn: 'Invalid ARN prefix: abcdef'"
}

I would like to get:

 {
   type: BadRequest
   status: "Incorrect body parameters"
  }

Description

I am not able to modify mapping template for 400 integration response. According to documentation there is no way to update the template separately for 200 & 400 responses.

My code:

        - http:
            path: endpoint/path
            method: POST
            action: DescribeExecution
            response:
              template:
                application/json: |-
                  #set($inputRoot = $input.path('$'))
                  {
                    "status": $inputRoot.status
                  }

This updates the 200 integration response. But I want to modify the template for 400 as well. I tried the standard statusCodes for serveless way but it does not work.

I tried according to serverless docs:

    - http:
            path: endpoint/path
            method: POST
            action: DescribeExecution
            response:
              template:
                application/json: |-
                  #set($inputRoot = $input.path('$'))
                  {
                    "status": $inputRoot.status
                  }
             statusCodes:
               200:
                 pattern: ""
               400:
                 pattern: '.*"statusCode":400,.*"
                 template:
                   application/json: |-
                      {
                        type: BadRequest
                        status: "Incorrect body parameters"
                      }
                     

I also tried to override the default gateway status codes for this, but it does not work (I overrided 4xx, 429, 400 for default gateway responses). I have default gateway responses for application/json defined as:

 {
   type: BadRequest
   status: "Incorrect body parameters"
  }

It still returns. Mapping template for 400 is not visibile in the aws console.

{
  "__type": "com.amazonaws.swf.service.v2.model#InvalidArn",
  "message": "Invalid Arn: 'Invalid ARN prefix: abcdef'"
}

If it occurrs that there is a way to do that, please UPDATE documentation, because it is a common usecase.