This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
The realm (and thus the DB connection) is used only when someone logs into an application. I doubt that it's going to be worth the trouble of dealing with a connection pool just for that. How many users are you expecting to sign in (not being logged in!) simultaneously over any extended period of time?