Replace "election_index" with "election_dir (u, ESIndex)"
Simplification of AUTH_INSTANCE

There were 3 phases: configuration parsing, service definition and
service registration. The last two can be merged, since there is no
direct external reference to the service of a specific auth system. As
a consequence, there is no need for a Register sub-fonctor in
AUTH_INSTANCE: service definition and registration occur directly in
the Make function, called by instantiate.
AUTH_INSTANCE specifies a service handler rather than a service
Generic login page when there are several auth instances