add possibility to customize the JSONResponse class for openapi.json

fastapi/applications.py

@@ -58,6 +58,7 @@ class FastAPI(Starlette):
         version: str = "0.1.0",
         openapi_url: Optional[str] = "/openapi.json",
         openapi_tags: Optional[List[Dict[str, Any]]] = None,
+        openapi_response_class: Type[JSONResponse] = JSONResponse,
         servers: Optional[List[Dict[str, Union[str, Any]]]] = None,
         dependencies: Optional[Sequence[Depends]] = None,
         default_response_class: Type[Response] = Default(JSONResponse),
@@ -100,6 +101,7 @@ class FastAPI(Starlette):
         self.license_info = license_info
         self.openapi_url = openapi_url
         self.openapi_tags = openapi_tags
+        self.openapi_response_class = openapi_response_class
         self.root_path_in_servers = root_path_in_servers
         self.docs_url = docs_url
         self.redoc_url = redoc_url
@@ -228,7 +230,7 @@ class FastAPI(Starlette):
                     if root_path and self.root_path_in_servers:
                         self.servers.insert(0, {"url": root_path})
                         server_urls.add(root_path)
-                return JSONResponse(self.openapi())
+                return self.openapi_response_class(self.openapi())
 
             self.add_route(self.openapi_url, openapi, include_in_schema=False)
         if self.openapi_url and self.docs_url: