[9] RFR: 8076117: EndEntityChecker should not process custom extensions after PKIX validation

[Jason Uh]

Please review this fix, which prevents redundant extension checking in 
EndEntityChecker.

When checking extensions in an end entity certificate, if 
sun.security.validator.EndEntityChecker comes across any extensions that 
are critical and unknown, it throws an exception, even if those 
extensions had already been checked by custom PKIXCertPathCheckers 
(specified in the PKIXParameters) earlier in the validation by 
PKIXValidator. This checking is not necessary when path validation is 
performed by a PKIXValidator.

However, if the validation is performed by a SimpleValidator, 
EndEntityChecker should continue to check extensions.

webrev: http://cr.openjdk.java.net/~juh/8076117/00/
bug: https://bugs.openjdk.java.net/browse/JDK-8076117

Thanks,
Jason