Refactor SSLUtils.loadKey using PEMParser

[exceptionfactory]

This pull request implements private key loading refactoring proposed in #2440.

The implementation refactors the SSLUtils.loadKey method to use the Bouncy Castle PEMParser for all types of private keys. The existing implementation uses PEMParser for ECDSA Private Keys, and the proposed changes eliminate the need for custom DER and PKCS8 parsing. Changes include updates to the SSLUtils test class, providing a reusable test method and also asserting expected algorithm values for parsed Private Keys.

[linux-foundation-easycla]

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[brendandburns]

Thanks for the PR. A couple of questions:
First, I'm curious about the motivation for the PR. It looks like a general cleanup and that's appreciated, but did you run into problems with the other code?

Second can I request that this is split into two PRs:

1. the refactor to SSLUtils
2. the refactor to the unit tests

The reason for this is that I want to make sure that the existing tests pass with the refactored SSL code. I worry that in refactoring both the implementation and the test at the same time it is possible for behaviors to regress.

Thanks!

[exceptionfactory]

Thanks for the quick reply @brendandburns!

I was reviewing the client code for its approach to loading private keys and came across issue #1724. I also noted the code comments with the try-catch approach to handling different algorithms with PKCS8. I haven't noticed any runtime issues, but I have worked on projects such as sshj to improve key loading.

I understand the concern about refactoring both the implementation and tests together. I will update this PR to remove the unit test updates and create a new PR for just those changes.

[brendandburns]

/lgtm
/approve

(assuming tests pass :)

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: brendandburns, exceptionfactory

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