Provide x509 auth support for Admin Server APIs

With adding snapshot and restore admin server commands, the scope of AdminServer APIs is expanded from “reading some data from the server” to “performing some operations on the server”. We would need provide auth support on AdminServer APIs.

The overall design is in https://docs.google.com/document/d/1UHf07ZnPi_Kyos7-DRnANmkuhv1BILNGJanZkBv12WA/edit?usp=sharing

This JIRA is to provide x509 auth support.