[coverage] Conformance findings: AUTH-012,AUTH-015

Start with the coverage PR diff under tests/, focusing on test_server_certificate_validation_enabled_by_default and test_mutual_tls_client_certificate_options_validated, then trace the Thrift and SEA connection paths they exercise. Done means both paths reject untrusted server certificates and incomplete or malformed client identity options with actionable TLS or client-key errors, without making OpenSession or CreateSession calls.

Summary

Surfaced by the multi-language coverage fan-out while conformance-testing these SPEC-IDs against databricks/databricks-sql-python. Each finding is committed as an expected-failure (xfail) test in the coverage PR — the test asserts the CORRECT (post-fix) behavior and stays red until THIS driver (databricks/databricks-sql-python) is fixed, then flips green as a tripwire.

Findings

• AUTH-012 [sea]: kernel (SEA) rejects the untrusted server cert but the error drops rustls's UnknownIssuer cause, reporting only "http request failed after N attempts: error sending request for url (…)" — a TLS-trust misconfiguration is indistinguishable from a network outage
  • failing test: test_server_certificate_validation_enabled_by_default (see the coverage PR diff under tests/)
• AUTH-015 [thrift]: mTLS client-identity options get no both-or-neither validation: an unpaired _tls_client_cert_file reaches SSLContext.load_cert_chain(certfile=…, keyfile=None) and surfaces OpenSSL's opaque "[SSL] PEM lib", naming neither the supplied option nor the missing private key
  • failing test: test_mutual_tls_client_certificate_options_validated (see the coverage PR diff under tests/)
• AUTH-012: kernel (SEA) backend rejects an untrusted server certificate but its error drops the rustls cause, reporting only "http request failed after N attempts: error sending request for url (…)" — a TLS-trust misconfiguration is indistinguishable from a network outage
• AUTH-015: mTLS client-identity options get no both-or-neither validation: an unpaired _tls_client_cert_file reaches load_cert_chain(certfile=…, keyfile=None) on the Thrift path and surfaces OpenSSL's opaque [SSL] PEM lib, naming neither the supplied option nor the missing private key

Reproduce & Expected

AUTH-012 — Verifies the driver is secure-by-default: with NO TLS options supplied, the driver performs full chain + hostname verification of the server certificate, and a server whose certificate does NOT chain…

Expected (per the shared spec):

• [thrift] exactly 0 OpenSession call(s)
• [sea] exactly 0 CreateSession call(s)
• full assertion contract:

result:
- error:
    contains:
    - certificate
    - cert
    - self-signed
    - self signed
    - unable to verify
    - unable to get local issuer
    - tls
    - ssl
    - handshake
protocol:
  thrift:
  - call_count:
      method: OpenSession
      expected: 0
  sea:
  - call_count:
      operation: CreateSession
      expected: 0

AUTH-015 — Verifies that the mutual-TLS (mTLS) client-identity options are validated on the client side with clear, actionable errors instead of failing opaquely deep in the TLS handshake.

Expected (per the shared spec):

• [thrift] exactly 0 OpenSession call(s)
• [sea] exactly 0 CreateSession call(s)
• full assertion contract:

result:
- label: both_or_neither
  error:
    contains:
    - client cert
    - clientcert
    - client key
    - clientkey
    - private key
    - mutual
    - mtls
    - both
- label: malformed_pem
  error:
    contains:
    - pem
    - certificate
    - client cert
    - clientcert
protocol:
  thrift:
  - call_count:
      method: OpenSession
      expected: 0
  sea:
  - call_count:
      operation: CreateSession
      expected: 0

Context

• The behavior was first fixed in a DIFFERENT driver — reference PR: https://github.com/databricks/databricks-sql-nodejs/pull/463 — which seeded the shared language-neutral spec. This issue tracks the same conformance gap in databricks/databricks-sql-python; the reference PR is for cross-referencing the intended behavior, NOT a change to this repo.
• Coverage PR carrying the reproducing xfail test(s): https://github.com/databricks/databricks-driver-test/pull/1115