Upload files to storage buckets with policies

const { data, error } = await supabase.storage
  .from('avatars')
  .upload(`${user.id}/avatar.png`, file, { upsert: true })

// public bucket
supabase.storage.from('avatars').getPublicUrl(path)
// private bucket: a link valid for one hour
await supabase.storage.from('invoices').createSignedUrl(path, 3600)

create policy "Users manage own folder" on storage.objects
  for all to authenticated
  using (bucket_id = 'avatars' and (storage.foldername(name))[1] = auth.uid()::text)
  with check (bucket_id = 'avatars' and (storage.foldername(name))[1] = auth.uid()::text);