Auto-update support for extensions
There was a recent policy decision to not allow individual extensions to auto-update (documentation/docs/dev!1165 (merged) , extensions/extensions-directory#48 (closed)). This issue is about creating core functionality that extensions could use to auto-update. The core functionality could enforce some standards to make this a transparent and secure process.
I propose that the core functionality enable any extension to ask site admins to opt-in to auto-updates. The default would be off, so explicit opt-in would be required. For auto-updates, I think it would make sense to require updates to be signed with a key that extension maintainer provides in some secure way.