Kerberos authentication for gremlin-server

Gremlin server would benefit from an explicit Kerberos authentication plugin, because preparing and maintaining such a plugin is nontrivial. Also, many other Apache project provide kerberized services.
In gremlin-console the standard Krb5LoginModule can be configured. Gremlin-server already includes the pluggable Sasl framework that can host the proposed Kerberos authentication plugin.