https://twitter.com/brianleroux/status/1577979058700578816

Default.yml

  DefaultWSLambda:
    Type: AWS::Serverless::Function
    Properties:
      Handler: index.handler
      CodeUri: "/var/task/src/ws/default"
      Runtime: nodejs16.x
  DefaultWSRoute:
    Type: AWS::ApiGatewayV2::Route
    Properties:
      ApiId:
        Ref: WS
      RouteKey: "$default"
      OperationName: DefaultWSRoute
      Target:
        Fn::Join:
        - "/"
        - - integrations
          - Ref: DefaultWSIntegration
  DefaultWSIntegration:
    Type: AWS::ApiGatewayV2::Integration
    Properties:
      ApiId:
        Ref: WS
      IntegrationType: AWS_PROXY
      IntegrationUri:
        Fn::Sub:
        - arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${DefaultWSLambda.Arn}/invocations
        - {}
  DefaultWSPermission:
    Type: AWS::Lambda::Permission
    DependsOn:
    - WS
    - DefaultWSLambda
    Properties:
      Action: lambda:InvokeFunction
      FunctionName:
        Ref: DefaultWSLambda
      Principal: apigateway.amazonaws.com