Auth: Support PKCS#1 RSA Private Keys for mTLS

[nbayati]

The Java mTLS key loading (SecurityUtils.createMtlsKeyStore) currently only supports PKCS#8 format (-----BEGIN PRIVATE KEY-----) private keys. This issue requests adding support for the older PKCS#1 format (-----BEGIN RSA PRIVATE KEY-----) to align with Go and Python implementations.

[lqiu96]

Going to move this to the http-client issues as this code exists inside there

A few additional questions:

1. Is this blocking anything for any mtls or x509 functionality? Would we consider this a nice-to-have or a blocker? If this is blocking, is there a deadline for this?
2. Is this something that the Auth/ Java team would be implementing or will this be from your team to implement?

[nbayati]

Going to move this to the http-client issues as this code exists inside there

A few additional questions:

1. Is this blocking anything for any mtls or x509 functionality? Would we consider this a nice-to-have or a blocker? If this is blocking, is there a deadline for this?
2. Is this something that the Auth/ Java team would be implementing or will this be from your team to implement?

Sounds good, moving this to the http-client issues makes sense, especially since the relevant code lives there.

To answer your questions:

I'd say this is a nice-to-have feature. In the worst-case scenario, customers would need to use a separate tool to update their certificates, which isn't ideal but also isn't a hard blocker for core mTLS or x509 functionality. There's no hard deadline for this.

Regarding implementation, this likely wouldn't be something our team handles. Given the source code is outside our usual scope, it seems more appropriate for the Auth/Java team to implement, as they would have the necessary context for changes within the http-client.