Using the given client, account and interactor (or interaction.Auto if nil), register the client account if it does not already exist.

Creates, fulfils and finalises an order.

Returns a list of indices to authz.Challenges, sorted by preference, most preferred first.

Any challenge having a preference at or below this value will never be used.

PreferFast prefers fast types.

Determines the degree to which a challenge is preferred.

TypePreferencer returns a preference according to the type of the challenge.