Define Env.* constant for all Env context variables
Replace the use of string (for e.g "#AD_User_ID") with Env.* constant.
Triaged by Matheus Marcelino.
I think it is a great idea. If I'm not wrong, doing this, only one reference is maintained per string by jvm. For e.g. searching throught the source code just by “#Date“, we have 101 matches.