The use case:

I'm running FastAPI behind a nginx reverse proxy, at the path http://localhost/api/. The documentation front ends (swagger and redoc) are expecting openapi.json at http://localhost/openapi.json but it's actually routed at http://localhost/api/openapi.json.

Setting openapi_url to /api/openapi.json also changes the openapi.json path, so now it's looking for (through the proxy) http://localhost/api/api/openapi.json.

Ideally, it'd be great if we could specify the "public path" for the api. That's how e.g. vue does it