Sync fastapi docs from 50fa3f7c on 2026-01-11

docs_src/behind_a_proxy/tutorial002_py39.py

@@ -0,0 +1,8 @@
+from fastapi import FastAPI, Request
+
+app = FastAPI(root_path="/api/v1")
+
+
+@app.get("/app")
+def read_main(request: Request):
+    return {"message": "Hello World", "root_path": request.scope.get("root_path")}