OkHttp ConnectionSpecs include TLSv1.3 without any compatible cipher suites

[yschimke]

See discussion on #4109

[yschimke]

Not a blocker, as JDK 11 detects this and handles gracefully.

With a mix of TLS 1.3 + 1.2 cipher suites

"ClientHello": {
  "client version"      : "TLSv1.2",
  "cipher suites"       : "[TLS_AES_128_GCM_SHA256(0x1301), TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384(0xC02C), TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256(0xC02B), TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384(0xC030), TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256(0xC02F)]",
    "supported_versions (43)": {
      "versions": [TLSv1.3, TLSv1.2]
    },

With TLS 1.3 + TLS 1.2 but TLS 1.2 cipher suites only
With TLS 1.2 and TLS 1.2 cipher suites only (this is new behaviour for TLSv1.2 specified in TLSv1.3 spec)

"ClientHello": {
  "client version"      : "TLSv1.2",
  "cipher suites"       : "[TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384(0xC02C), TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256(0xC02B), TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384(0xC030), TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256(0xC02F)]",
    "supported_versions (43)": {
      "versions": [TLSv1.2]
    },

[yschimke]

Documented in the TLS 1.3 Spec

Updates Affecting TLS 1.2

This document defines several changes that optionally affect
implementations of TLS 1.2, including those which do not also support
TLS 1.3:

• A version downgrade protection mechanism is described in
  Section 4.1.3.

• RSASSA-PSS signature schemes are defined in Section 4.2.3.

• The "supported_versions" ClientHello extension can be used to
  negotiate the version of TLS to use, in preference to the
  legacy_version field of the ClientHello.

• The "signature_algorithms_cert" extension allows a client to
  indicate which signature algorithms it can validate in X.509
  certificates