fix signout redirect for oauth

backend/open_webui/routers/auths.py

@@ -687,7 +687,7 @@ async def signout(request: Request, response: Response):
                                     status_code=200,
                                     content={
                                         "status": True,
-                                        "redirect_url": f"{logout_url}?id_token_hint={oauth_id_token}",
+                                        "redirect_url": f"{logout_url}?id_token_hint={oauth_id_token}" + (f"&post_logout_redirect_uri={WEBUI_AUTH_SIGNOUT_REDIRECT_URL}" if WEBUI_AUTH_SIGNOUT_REDIRECT_URL else ""),
                                     },
                                     headers=response.headers,
                                 )