Implement a remote user import process

This adds a feature for remote authentication methods for clients, such as
LDAP, which will, after successful authentication, yield a
ClientCreateRequest rather than an AuthenticatedUser. The
ClientCreateRequest represents a successful authentication and user
information lookup for a remote client. The client is then presented with a
registration page where their information for their account in the local
system can be reviewed prior to the account creation. Once created, the
client account is confirmed without an email confirmation and is logged in
immediately without reentering a password.