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

WS.yml

WS:
  Type: AWS::ApiGatewayV2::Api
  Properties:
    Name: MyappWebsocketStaging
    ProtocolType: WEBSOCKET
    RouteSelectionExpression: "$request.body.message"
WebsocketDeployment:
  Type: AWS::ApiGatewayV2::Deployment
  DependsOn:
  - ConnectWSRoute
  - DefaultWSRoute
  - DisconnectWSRoute
  Properties:
    ApiId:
      Ref: WS
WebsocketStage:
  Type: AWS::ApiGatewayV2::Stage
  Properties:
    StageName: staging
    DeploymentId:
      Ref: WebsocketDeployment
    ApiId:
      Ref: WS
WebSocketPolicy:
  Type: AWS::IAM::Policy
  DependsOn: Role
  Properties:
    PolicyName: ArcWebSocketPolicy
    PolicyDocument:
      Statement:
      - Effect: Allow
        Action:
        - execute-api:Invoke
        - execute-api:ManageConnections
        Resource:
        - Fn::Sub:
          - arn:aws:execute-api:${AWS::Region}:*:${api}/*
          - api:
              Ref: WS
    Roles:
    - Ref: Role