RFR: 8326949: Authorization header is removed when a proxy Authenticator is set on HttpClient

[Michael McMahon]

Hi,

I closed https://github.com/openjdk/jdk/pull/21249 and am continuing the review on this PR.

This fix relaxes the constraints on user set authentication headers. Currently, any user set authentication headers are filtered out, if the HttpClient has an Authenticator set. The reason being that the authenticator is expected to manage authentication. With this fix, it will be possible to use pre-emptive authentication through user set headers, even if an authenticator is set. The expected use case is where the authenticator would manage either proxy or server authentication and the user set headers would manage server authentication if the authenticator is managing proxy (or vice versa).

A CSR will be filed to document this change.

Thanks,
Michael

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Commit messages:
 - implementation carried over from PR 21249

Changes: https://git.openjdk.org/jdk/pull/21408/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21408&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8326949
  Stats: 644 lines in 10 files changed: 439 ins; 202 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/21408.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21408/head:pull/21408

PR: https://git.openjdk.org/jdk/pull/21408