Groupon API
Groupon's own public API gateway. Live and Groupon-operated (responses carry x-brand: groupon and Envoy/GCP upstream headers), but gated: every path, including /v2/deals.json, /graphql and /.well-known/*, returns HTTP 401 with {"error":{"httpCode":401,"message":"'client_id' is invalid"}} until a valid client_id query parameter is supplied. Because the gateway returns the same 401 for paths that do not exist, its operation set could not be enumerated anonymously and no OpenAPI has been derived for it.