### What needs to get done In the provider service, when creating an instance, send a callback to craft-providers (see: https://github.com/canonical/craft-providers/issues/665). The default implementation of this callback should use the config service to get the app's `apt_proxy` configuration and use it to configure the proxy in apt. This is roughly what's done in https://github.com/canonical/craft-application/blob/c971a6098d5c3b93787bca217090af885088e626/craft_application/fetch.py#L388-L405 When doing this, have the fetch service use this. ### Why it needs to get done Allow apt proxies in craft apps