openapi: 3.0.1
info:
   title: test
   version: "0.1"
paths:
  /test:
    post:
      operationId: myOp
      responses:
        default:
          description: ok
      callbacks:
        subscription:
          http://$request.query.url:
            post:
              description: myCallback
              parameters:
              - name: myParam
                in: query
                schema:
                  type: string
              responses:
                default:
                  description: ok