types: add TLS constants

types: distinguish between human and Envoy serialization for TLSVersion constants

types: add DeprecatedAgentTLSVersions for backwards compatibility

types: add methods for printing TLSVersion as strings

types: add TLSVersionInvalid error value

types: add a basic test for TLSVersion comparison

types/tls.go

@@ -0,0 +1,93 @@
+package types
+
+// TLSVersion is a strongly-typed int used for relative comparison
+// (minimum, maximum, greater than, less than) of TLS versions
+type TLSVersion int
+
+const (
+	// Error value, excluded from lookup maps
+	TLSVersionInvalid TLSVersion = iota - 1
+
+	// Explictly allow implementation to select TLS version
+	// May be useful to supercede defaults specified at a higher layer
+	TLSVersionAuto
+
+	_ // Placeholder for SSLv3, hopefully we won't have to add this
+
+	// TLS versions
+	TLSv1_0
+	TLSv1_1
+	TLSv1_2
+	TLSv1_3
+)
+
+var (
+	TLSVersions = map[string]TLSVersion{
+		"TLS_AUTO": TLSVersionAuto,
+		"TLSv1_0":  TLSv1_0,
+		"TLSv1_1":  TLSv1_1,
+		"TLSv1_2":  TLSv1_2,
+		"TLSv1_3":  TLSv1_3,
+	}
+	// NOTE: This interface is deprecated in favor of TLSVersions
+	// and should be eventually removed in a future release.
+	DeprecatedAgentTLSVersions = map[string]TLSVersion{
+		"":      TLSVersionAuto,
+		"tls10": TLSv1_0,
+		"tls11": TLSv1_1,
+		"tls12": TLSv1_2,
+		"tls13": TLSv1_3,
+	}
+	HumanTLSVersionStrings = map[TLSVersion]string{
+		TLSVersionAuto: "Allow implementation to select TLS version",
+		TLSv1_0:        "TLS 1.0",
+		TLSv1_1:        "TLS 1.1",
+		TLSv1_2:        "TLS 1.2",
+		TLSv1_3:        "TLS 1.3",
+	}
+	EnvoyTLSVersionStrings = map[TLSVersion]string{
+		TLSVersionAuto: "TLS_AUTO",
+		TLSv1_0:        "TLSv1_0",
+		TLSv1_1:        "TLSv1_1",
+		TLSv1_2:        "TLSv1_2",
+		TLSv1_3:        "TLSv1_3",
+	}
+)
+
+func (v TLSVersion) String() string {
+	return HumanTLSVersionStrings[v]
+}
+
+func (v TLSVersion) EnvoyString() string {
+	return EnvoyTLSVersionStrings[v]
+}
+
+// The naming convention for cipher suites changed in TLS 1.3
+// but constant values should still be globally unqiue
+// Handling validation on a subset of TLSCipherSuite constants
+// would be a future exercise if cipher suites for TLS 1.3 ever
+// become configurable in BoringSSL, Envoy, or other implementation
+type TLSCipherSuite string
+
+// IANA cipher suite constants
+// NOTE: This is the total list of TLS 1.2-style cipher suites
+// which are currently supported by Envoy 1.21 and may change
+// as some older suites are removed in future Envoy releases
+// and Consul drops support for older Envoy versions
+// TODO: Is there any better/less verbose way to handle this mapping?
+const (
+	ECDHE_ECDSA_AES128_GCM_SHA256 TLSCipherSuite = "ECDHE-ECDSA-AES128-GCM-SHA256"
+	ECDHE_ECDSA_CHACHA20_POLY1305                = "ECDHE-ECDSA-CHACHA20-POLY1305"
+	ECDHE_RSA_AES128_GCM_SHA256                  = "ECDHE-RSA-AES128-GCM-SHA256"
+	ECDHE_RSA_CHACHA20_POLY1305                  = "ECDHE-RSA-CHACHA20-POLY1305"
+	ECDHE_ECDSA_AES128_SHA                       = "ECDHE-ECDSA-AES128-SHA"
+	ECDHE_RSA_AES128_SHA                         = "ECDHE-RSA-AES128-SHA"
+	AES128_GCM_SHA256                            = "AES128-GCM-SHA256"
+	AES128_SHA                                   = "AES128-SHA"
+	ECDHE_ECDSA_AES256_GCM_SHA384                = "ECDHE-ECDSA-AES256-GCM-SHA384"
+	ECDHE_RSA_AES256_GCM_SHA384                  = "ECDHE-RSA-AES256-GCM-SHA384"
+	ECDHE_ECDSA_AES256_SHA                       = "ECDHE-ECDSA-AES256-SHA"
+	ECDHE_RSA_AES256_SHA                         = "ECDHE-RSA-AES256-SHA"
+	AES256_GCM_SHA384                            = "AES256-GCM-SHA384"
+	AES256_SHA                                   = "AES256-SHA"
+)

types/tls_test.go

@@ -0,0 +1,24 @@
+package types
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestTLSVersion_PartialEq(t *testing.T) {
+	require.Greater(t, TLSv1_3, TLSv1_2)
+	require.Greater(t, TLSv1_2, TLSv1_1)
+	require.Greater(t, TLSv1_1, TLSv1_0)
+
+	require.Less(t, TLSv1_2, TLSv1_3)
+	require.Less(t, TLSv1_1, TLSv1_2)
+	require.Less(t, TLSv1_0, TLSv1_1)
+}
+
+func TestTLSVersion_Invalid(t *testing.T) {
+	require.NotEqual(t, TLSVersionAuto, TLSVersionInvalid)
+
+	// Error values should be negative
+	require.Less(t, TLSVersionInvalid, 0)
+}