You can use below node package to create and deploy proxy https://github.com/anil614sagar/openapi2apigee

You can use externalValue tag to refer the json filehttps://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.0.2.md#user-content-exampleexternalvalue

@YuriAbaev - You will get isSuccess() = True on 4xx & 5xx because connection is established and you got the response back from backend