Function add_member 

pub async fn add_member(
    read: &Read,
    clock: &Clock,
    email: Email,
    area: &str,
) -> Result<MemberAdded>

An address no account holds gets one without a password, which signs in once its owner sets one (password-reset), follows a sign-in link or connects a provider. An account already a member keeps its membership, so adding it again changes nothing but a role. An account adopted, or given a role, whose address nobody proved may have been signed up by someone else expecting this, so it is distrusted.