Specify content-type in API Gateway method response using CDK

Question

I am creating proxy API gateway to non-public S3 bucket using CDK. The S3 bucket contains html, javascript, and css files.

I created an api using CDK like this:

const api = new apigw.RestApi(this, 'Test-Web')

api.root
  .addResource('{file}')
  .addMethod('GET', new apigw.AwsIntegration({
    service: 's3',
    integrationHttpMethod: 'GET',
    path: `${bucket.bucketName}/{file}`,
    options: {
      credentialsRole: role,
      requestParameters: {
        'integration.request.path.file': 'method.request.path.file'
      },
      integrationResponses: [{
        statusCode: '200'
      }]
    }
  }), {
    requestParameters: {
      'method.request.path.file': true
    },
    methodResponses: [{
      statusCode: '200'
    }]
  })

It works fine, but has a problem. The content type of the response is always set to application/json. I could see that the content type of integration responses (responses from S3) varies from text/html to text/css, application/javascript depending on the file.

How can I set this API to return correct content type on each file by passing the same content type header value of integration response to method response? Best if I can pass the content-type header from S3 as it already returns correctly.

Answer 1

CDK documentation is not great. I managed to find a solution: I had to add responseParameters in integrationResponses to set Content-Type header from S3 to API gateway response. Please see below, especially the line marked with <<<--.

api.root
  .addResource('{file}')
  .addMethod(
    'GET',
    new apigw.AwsIntegration({
      service: 's3',
      integrationHttpMethod: 'GET',
      path: `${bucket.bucketName}/{file}`,
      options: {
        credentialsRole: role,
        requestParameters: {
          'integration.request.path.file': 'method.request.path.file'
        },
        integrationResponses: [{
          statusCode: '200',
          selectionPattern: '2..',
          responseParameters: {
            'method.response.header.Content-Type': 'integration.response.header.Content-Type' // <<<--
          },
        }, {
          statusCode: '403',
          selectionPattern: '4..'
        }]
      }
    }), {
      requestParameters: {
        'method.request.path.file': true
      },
      methodResponses: [{
        statusCode: '200',
        responseParameters: {
          'method.response.header.Content-Type': true // <<<-- 
        }
      }, {
        statusCode: '404'
      }]
    })