RFR: 8281561: Disable http DIGEST mechanism with MD5 and SHA-1 by default [v7]

[Michael McMahon]

> Hi,
> 
> Could I get the following change reviewed please, which is to disable the MD5 message digest algorithm by default in the HTTP Digest authentication mechanism? The algorithm can be opted into by setting a new system property "http.auth.digest.reEnabledAlgs" to include the value MD5. The change also updates the Digest authentication implementation to use some of the more secure features defined in RFC7616, such as username hashing and additional digest algorithms like SHA256 and SHA512-256.
> 
> - Michael

Michael McMahon has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 22 additional commits since the last revision:

 - latest update
 - Merge branch 'master' into md5
 - delete .swp file
 - incomplete test update
 - made disabledAlgorithms immutable
 - Merge branch 'master' into md5
 - update after third review round
 - removed swp file
 - update after second review round
 - update
 - ... and 12 more: https://git.openjdk.java.net/jdk/compare/7047a23e...2ef5636d

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7688/files
  - new: https://git.openjdk.java.net/jdk/pull/7688/files/66c320ce..2ef5636d

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7688&range=06
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7688&range=05-06

  Stats: 7185 lines in 421 files changed: 3921 ins; 1034 del; 2230 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7688.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7688/head:pull/7688

PR: https://git.openjdk.java.net/jdk/pull/7688