OPTIONS refers to pre-requests that are sent to servers by clients. Generally, you can use these requests to check whether clients have permission to perform operations on servers. Only after a pre-request is returned successfully, clients start to execute the follow-up requests.
OBS allows buckets to store static web resources. The buckets of OBS can serve as website resources if the buckets are properly used. In this scenario, buckets in OBS serve as servers to process OPTIONS pre-requests from clients.
OBS can process OPTIONS pre-requests only after CORS is configured for buckets in OBS. For details about CORS, see section PUT Bucket CORS.