Uses the clientutil.Backend abstraction for the user-meta-server
client API.

Useful for partitioned (sharded) services that need to make
partition-related decisions at authentication time.

Starting with counters for authentication requests, split by service
and status.

Log errors, and drop unnecessary replies when shutting down a
connection.

Upstream changed the New parameters

Still does not send out "new device" emails, but there are hooks to do
so.

Drop the {crypt} prefix from LDAP-encrypted passwords, if present

Turn Server into a Client with a small interface wrapper.