* refactoring config

* Update by comments

token is the current token comparison, and oidc generates oidc token using client-credentials flow. in addition - add ping verification using the same method

The ClientCommonConf, configuration file path, and server UDP port are
now passed around as arguments instead of being shared between
components as global variables. This allows for multiple clients to
exist in the same process, and allows client.Session to be used as a
library more easily.

whether it's success or fail, otherwise it will cause memory leak
ref: https://golang.org/pkg/net/http/

udp