Callback delegate for custom certificate verification.
Called after standard verification (if any) completes, with its outcome in TlsVerifyInfo.standardVerification. The callback is invoked even when standard verification failed, so pin-auditing can observe every chain.
Override semantics: returning true ACCEPTS the connection even when standardVerification == FAILED (this is what enables self-signed and pinning flows — use deliberately); returning false always rejects, failing the handshake as TlsProgress.ERROR with a CERTIFICATE_ERROR lastError (the handshake itself never throws).
Use cases:
- Certificate pinning (SHA-256 fingerprint, public key pinning)
- Corporate proxy environments with custom CAs
- Development environments with self-signed certificates
- Audit logging of the full certificate chain