[jdk11u-dev] RFR: 8268617: [REDO] backport to 11u of 8236859: WebSocket over ...

[Larry-N]

Backport of 8236859: WebSocket over authenticating proxy fails with NPE
The patch doesn't apply cleanly, manually merged `AuthenticationFilter.java, HttpResponseImpl.java`, corrected @library path and import statement in `WebSocketProxyTest.java`

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Commit messages:
 - 8268617: [REDO] backport to 11u of 8236859: WebSocket over authenticating proxy fails with NPE

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/29/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=29&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268617
  Stats: 936 lines in 12 files changed: 898 ins; 5 del; 33 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/29.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/29/head:pull/29

PR: https://git.openjdk.java.net/jdk11u-dev/pull/29