Please review the code change at http://cr.openjdk.java.net/~weijun/8058290/webrev.00/
After this fix, a "renewTGT=true" in JAAS config for Krb5LoginModule means "renew if old enough", as suggested by the bug reporter [1].
Thanks Max [1] https://bugs.openjdk.java.net/browse/JDK-8058290