RFR: 8304818: Prune HttpURLConnection cache when corresponding Authenticator is garbage collected

[Michael McMahon]

Hi,

Can I get a review for this please? This change uses a Cleaner to check when java.net.Authenticator instances become unreachable, and then prunes the authentication cache for entries that correspond to that Authenticator and therefore cannot be used again. This stops the authentication cache from growing in size unbounded. Note, this only happens in the probably unusual case where more than one Authenticator object is used. Normally there is no reason to use more than one instance.

Thanks,
Michael.

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Commit messages:
 - revert removed methods (used in tests)
 - initial impl

Changes: https://git.openjdk.org/jdk/pull/13159/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13159&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304818
  Stats: 242 lines in 4 files changed: 239 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/13159.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13159/head:pull/13159

PR: https://git.openjdk.org/jdk/pull/13159