RFR: 8284910: Buffer clean in PasswordCallback

[Xue-Lei Andrew Fan]

Please review this password cleanup enhancement in the PasswordCallback implementation.  This is one of the effort to clean up the buffered passwords.

The PasswordCallback.setPassword() clones the password, but is not registered for cleanup. An application could call clearPassword() for the purpose, but it would be nice to cleanup the buffer as well if clearPassword() was not called in an application. And, if the setPassword() get called multiple times, the clearPassword() should also be called the same times if not relying on finalization. It could be fragile in practice.

-------------

Commit messages:
 - 8284910: Buffer clean in PasswordCallback

Changes: https://git.openjdk.java.net/jdk/pull/8272/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8272&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284910
  Stats: 142 lines in 3 files changed: 136 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8272.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8272/head:pull/8272

PR: https://git.openjdk.java.net/jdk/pull/8272