Close every backend.
One backend that spans every enabled provider, for the NAP dm service.
Enable a provider. Throws unavailable:<reason> when it cannot run.
Forget what the user settled for one person, or for everyone when no key is given.
Optionalpubkey: stringEvery provider, in the user's order.
Put an enabled provider first.
Reorder the providers; ids left out keep their relative order after the ones named.
Registry of providers; the shell holds exactly one.