[macastelaz]

Summary

Verifies that the parsed PrivateKey cryptographically matches the leaf X509Certificate's PublicKey in MtlsKeyStoreUtils.createMtlsKeyStore(), and adds retry handling (3 attempts with a 100ms backoff, matching AgentIdentityUtils.loadAndVerifyCredentials()) in X509Provider.getKeyStore() when loading separate cert_path and key_path files from disk.

Problem

1. Unverified KeyStore entries: KeyStore.getInstance("JKS").setKeyEntry("alias", key, new char[] {}, chain) does not verify that key corresponds to chain[0].getPublicKey() as long as the key algorithm matches (e.g., both are RSA or both are EC).
2. Non-atomic rotation across separate cert_path and key_path files: When an external certificate rotator updates cert_path (cert_A -> cert_B) slightly before key_path (key_A -> key_B), transport channel refresh (CertificateRotationTracker, which tracks cert_path's SHA-256 fingerprint) can trigger X509Provider.getKeyStore() during the intermediate (cert_B, key_A) window. Without key-pair verification and retries, getKeyStore() succeeds with a mismatched KeyStore and the channel marks FP(cert_B) as refreshed, leaving the mTLS channel with a mismatched certificate and private key until the next rotation.

Solution

• MtlsKeyStoreUtils.createMtlsKeyStore(): Perform a test signature and verification (SHA256withRSA for RSA keys, SHA256withECDSA for EC/ECDSA keys with SunEC "ECDSA" -> "EC" public key normalization) to ensure the parsed private key matches the leaf certificate's public key, throwing GeneralSecurityException("Certificate and private key do not match") on mismatch.
• X509Provider.getKeyStore(): Retry up to 3 times (100ms interval) when reading and verifying separate cert_path and key_path files from WorkloadCertificateConfiguration, handling transient mid-rotation key mismatches or partial file writes while preserving interrupt restoration on InterruptedException.

Testing

• Added unit tests in MtlsKeyStoreUtilsTest covering mismatched RSA and EC key pairs.
• Added unit tests in X509ProviderTest covering:
  • Retrying and succeeding when key_path finishes rotating to match cert_path on a subsequent attempt.
  • Failing with IOException caused by GeneralSecurityException("Certificate and private key do not match") after exhausting all 3 attempts.
  • Retrying and succeeding when cert_path is transiently empty/truncated on the first attempt.
  • Restoring the thread interrupt flag and failing fast with IOException if interrupted during retry backoff.

[gemini-code-assist]

Code Review

This pull request introduces key pair verification when creating an mTLS KeyStore to ensure the private key matches the leaf certificate's public key. It also adds retry logic in X509Provider to handle transient mismatches during atomic key rotations. The review feedback recommends separating cryptographic setup/execution failures from actual key verification mismatches to prevent misleading error messages, and advises against adding out-of-scope algorithm normalization (such as converting 'ECDSA' to 'EC') to maintain behavioral alignment.