FastAPI で特定のルートのエラー応答をカスタマイズするにはどうすればよいですか?

from fastapi import FastAPI, Request, Header, status
from fastapi.exceptions import RequestValidationError
from fastapi.responses import JSONResponse
from fastapi.encoders import jsonable_encoder

app = FastAPI()
routes_with_custom_exception = ['/']

@app.exception_handler(RequestValidationError)
async def validation_exception_handler(request: Request, exc: RequestValidationError):
    if request.url.path in routes_with_custom_exception:
        # check whether the error relates to the `some_custom_header` parameter
        for err in exc.errors():
            if err['loc'][0] == 'header' and err['loc'][1] == 'some-custom-header':
                return JSONResponse(content={'401': 'Unauthorized'}, status_code=401)
            
    return JSONResponse(
        status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
        content=jsonable_encoder({'detail': exc.errors(), 'body': exc.body}),
    )

# main API
app = FastAPI()

# sub-application with custom error handling
subapi = FastAPI()
@subapi.exception_handler(RequestValidationError)
async def validation_exception_handler(request: Request, exc: RequestValidationError):
    # Handle error specific to sub-application's routes
    return JSONResponse(content={'401': 'Unauthorized'}, status_code=401)

# mount sub-application
app.mount('/sub', subapi)

from fastapi import FastAPI, APIRouter, APIRoute, Request, Header, HTTPException
from fastapi.responses import JSONResponse
from fastapi.exceptions import RequestValidationError

class ValidationErrorHandlingRoute(APIRoute):
    def get_route_handler(self) -> Callable:
        original_route_handler = super().get_route_handler()

        async def custom_route_handler(request: Request) -> Response:
            try:
                return await original_route_handler(request)
            except RequestValidationError as e:
                raise HTTPException(status_code=401, detail='401 Unauthorized')

# create new router with custom error handling
router = APIRouter(route_class=ValidationErrorHandlingRoute)

# add custom error handling to router
@router.get('/custom')
async def custom_route(some_custom_header: str = Header(...)):
    return {'some-custom-header': some_custom_header}

# add router to app 
app.include_router(router)