Currently, it happens to be S3 to S3, but you could write an adapter, let's say GoogleCloudStorage and it will become S3 -> GoogleCloudStorage, or any other type of underline Storage.

Additionally, we provide a special way of authenticating to Supabase S3 using the SessionToken, which allows you to scope S3 operations to your users specific access control

https://supabase.com/docs/guides/storage/s3/authentication#s...