Set up gateway response customization in OpenAPI

You can use the x-amazon-apigateway-gateway-responses extension at the API root level to customize gateway responses in OpenAPI. The following OpenAPI definition shows an example for customizing the GatewayResponse of the MISSING_AUTHENTICATION_TOKEN type.

  "x-amazon-apigateway-gateway-responses": {
    "MISSING_AUTHENTICATION_TOKEN": {
      "statusCode": 404,
      "responseParameters": {
        "gatewayresponse.header.x-request-path": "method.input.params.petId",
        "gatewayresponse.header.x-request-query": "method.input.params.q",
        "gatewayresponse.header.Access-Control-Allow-Origin": "'a.b.c'",
        "gatewayresponse.header.x-request-header": "method.input.params.Accept"
      },
      "responseTemplates": {
        "application/json": "{\n     \"message\": $context.error.messageString,\n     \"type\":  \"$context.error.responseType\",\n     \"stage\":  \"$context.stage\",\n     \"resourcePath\":  \"$context.resourcePath\",\n     \"stageVariables.a\":  \"$stageVariables.a\",\n     \"statusCode\": \"'404'\"\n}"
      }
    }

In this example, the customization changes the status code from the default (403) to 404. It also adds to the gateway response four header parameters and one body mapping template for the application/json media type.