class ActiveStorage::Variant

for its redirection.
for a variant that points to the ActiveStorage::RepresentationsController, which in turn will use this +service_call+ method
Use url_for(variant) (or the implied form, like +link_to variant+ or +redirect_to variant+) to get the stable URL

it allows permanent URLs that redirect to the +service_url+ to be cached in the view.
Hiding the +service_url+ behind a redirect also gives you the power to change services without updating all URLs. And
with users. Instead, the +service_url+ should only be exposed as a redirect from a stable, possibly authenticated URL.
Returns the URL of the variant on the service. This URL is intended to be short-lived for security and not used directly

def service_url(expires_in: service.url_expires_in, disposition: :inline)
  service.url key, expires_in: expires_in, disposition: disposition, filename: filename, content_type: content_type
end