RFR: 8270137: Kerberos Credential Retrieval from Cache not Working in Cross-Realm Setup [v2]

[Martin Balao]

> I'd like to propose a fix for JDK-8270137 [1].
> 
> This bug is triggered when using a previously stored referral ticket (in the Referrals Cache) at the moment of following a S4U2Proxy cross-realm referral. The mistakenly-used referral ticket matched the client and service names but it was obtained as a result of a non-S4U2Proxy request. In fact, it was the middle service that got it while trying to determine the backend service realm in a previous S4U2Proxy communication. The mistakenly-used referral ticket was not bind to the impersonated user (in other words, it was not obtained attaching the user's TGS as part of a S4U2Proxy request) and, thus, must not be used.
> 
> Even when one possible approach to fix this issue could be to be more selective at the moment of getting referral tickets from the Cache (that is: do not get anything from the Cache if it's for a S4U2Proxy request), I decided to go one step further and enhance the Referrals Cache. With this enhancement, we add more information to the stored referral tickets such as a footprint of the TGS (in the case of S4U2Proxy requests) or the user principal (in the case of S4U2Self requests). We now allow to store S4U2Proxy and S4U2Self referrals tickets but those will be re-used only if there is a perfect match of the TGS or user principal. As an example, if a middle service tries to replicate the exact S4U2Self communication for exactly the same user, cached referral tickets should be okay. With this enhancement, we increase the use of the Cache and the performance (time, network resources, etc.).
> 
> The ReferralsTest is enhanced to reflect these new scenarios and now uses cached S4U2Proxy/S4U2Self referral tickets.
> 
> No regressions observed in jdk/sun/security/krb5.
> 
> --
> [1] - https://bugs.openjdk.java.net/browse/JDK-8270137

Martin Balao has updated the pull request incrementally with one additional commit since the last revision:

  Variable renaming for clarity and unused parameter removed.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5036/files
  - new: https://git.openjdk.java.net/jdk/pull/5036/files/4260067e..4cb4b3e0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5036&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5036&range=00-01

  Stats: 12 lines in 1 file changed: 0 ins; 0 del; 12 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5036.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5036/head:pull/5036

PR: https://git.openjdk.java.net/jdk/pull/5036