feat: Introduce curve support to tls config

README.md

@@ -174,6 +174,8 @@ Usage of ./observatorium-api:
     	Comma-separated list of cipher suites for the server. Values are from tls package constants (https://golang.org/pkg/crypto/tls/#pkg-constants). If omitted, the default Go cipher suites will be used. Note that TLS 1.3 ciphersuites are not configurable.
   -tls.client-auth-type string
     	Policy for TLS client-side authentication. Values are from ClientAuthType constants in https://pkg.go.dev/crypto/tls#ClientAuthType (default "RequestClientCert")
+  -tls.curve-preferences string
+    	Comma-separated list of key exchange groups for the server. Values are IANA "TLS Supported Groups" names (e.g. X25519, secp256r1, X25519MLKEM768); Go crypto/tls constant names (e.g. CurveP256) are also accepted for the classic curves. If omitted, the default Go groups will be used. The list is a filter of allowed groups; crypto/tls chooses the preference order.
   -tls.healthchecks.server-ca-file string
     	File containing the TLS CA against which to verify servers. If no server CA is specified, the client will use the system certificates.
   -tls.healthchecks.server-name string

main.go

@@ -126,11 +126,12 @@ type serverConfig struct {
 }
 
 type tlsConfig struct {
-	minVersion     string
-	maxVersion     string
-	cipherSuites   []string
-	clientAuthType string
-	reloadInterval time.Duration
+	minVersion       string
+	maxVersion       string
+	cipherSuites     []string
+	curvePreferences []string
+	clientAuthType   string
+	reloadInterval   time.Duration
 
 	serverCertFile string
 	serverKeyFile  string
@@ -894,6 +895,7 @@ func main() {
 			cfg.tls.maxVersion,
 			cfg.tls.clientAuthType,
 			cfg.tls.cipherSuites,
+			cfg.tls.curvePreferences,
 		)
 		if err != nil {
 			stdlog.Fatalf("failed to initialize tls config: %v", err)
@@ -1004,6 +1006,7 @@ func main() {
 			cfg.tls.maxVersion,
 			cfg.tls.clientAuthType,
 			cfg.tls.cipherSuites,
+			cfg.tls.curvePreferences,
 		)
 		if err != nil {
 			stdlog.Fatalf("failed to initialize tls config: %v", err)
@@ -1108,6 +1111,7 @@ func (m *multiStringFlag) String() string {
 func parseFlags() (config, error) {
 	var (
 		rawTLSCipherSuites             string
+		rawTLSCurvePreferences         string
 		rawMetricsReadEndpoint         string
 		rawMetricsWriteEndpoint        string
 		rawMetricsRulesEndpoint        string
@@ -1277,6 +1281,12 @@ func parseFlags() (config, error) {
 			" Values are from tls package constants (https://golang.org/pkg/crypto/tls/#pkg-constants)."+
 			" If omitted, the default Go cipher suites will be used."+
 			" Note that TLS 1.3 ciphersuites are not configurable.")
+	flag.StringVar(&rawTLSCurvePreferences, "tls.curve-preferences", "",
+		"Comma-separated list of key exchange groups for the server."+
+			" Values are IANA \"TLS Supported Groups\" names (e.g. X25519, secp256r1, X25519MLKEM768);"+
+			" Go crypto/tls constant names (e.g. CurveP256) are also accepted for the classic curves."+
+			" If omitted, the default Go groups will be used."+
+			" The list is a filter of allowed groups; crypto/tls chooses the preference order.")
 	flag.StringVar(&cfg.tls.clientAuthType, "tls.client-auth-type", "RequestClientCert",
 		"Policy for TLS client-side authentication. Values are from ClientAuthType constants in https://pkg.go.dev/crypto/tls#ClientAuthType")
 	flag.DurationVar(&cfg.tls.reloadInterval, "tls.reload-interval", time.Minute,
@@ -1485,6 +1495,9 @@ func parseFlags() (config, error) {
 	if rawTLSCipherSuites != "" {
 		cfg.tls.cipherSuites = strings.Split(rawTLSCipherSuites, ",")
 	}
+	if rawTLSCurvePreferences != "" {
+		cfg.tls.curvePreferences = strings.Split(rawTLSCurvePreferences, ",")
+	}
 
 	return cfg, nil
 }
@@ -1618,6 +1631,7 @@ func newGRPCServer(cfg *config, tenantHeader string, tenantIDs map[string]string
 			cfg.tls.maxVersion,
 			cfg.tls.clientAuthType,
 			cfg.tls.cipherSuites,
+			cfg.tls.curvePreferences,
 		)
 		if err != nil {
 			return nil, fmt.Errorf("failed to create gRPC TLS config: %w", err)

tls/config.go

@@ -8,8 +8,26 @@ import (
 	"github.com/go-kit/log/level"
 )
 
+// curveIDs maps supported key-exchange group names to crypto/tls CurveIDs.
+// Both IANA names and Go crypto/tls constant names are accepted.
+var curveIDs = map[string]tls.CurveID{
+	// X25519 and the ML-KEM hybrids: IANA name == Go constant name.
+	"X25519":             tls.X25519,
+	"X25519MLKEM768":     tls.X25519MLKEM768,
+	"SecP256r1MLKEM768":  tls.SecP256r1MLKEM768,
+	"SecP384r1MLKEM1024": tls.SecP384r1MLKEM1024,
+
+	// Classic EC curves: IANA name (preferred) and Go constant name (alias).
+	"secp256r1": tls.CurveP256,
+	"secp384r1": tls.CurveP384,
+	"secp521r1": tls.CurveP521,
+	"CurveP521": tls.CurveP521,
+	"CurveP256": tls.CurveP256,
+	"CurveP384": tls.CurveP384,
+}
+
 // NewServerConfig provides new server TLS configuration.
-func NewServerConfig(logger log.Logger, certFile, keyFile, minVersion, maxVersion, clientAuthType string, cipherSuites []string) (*tls.Config, error) {
+func NewServerConfig(logger log.Logger, certFile, keyFile, minVersion, maxVersion, clientAuthType string, cipherSuites, curvePreferences []string) (*tls.Config, error) {
 	if certFile == "" && keyFile == "" {
 		level.Info(logger).Log("msg", "TLS disabled; key and cert must be set to enable")
 
@@ -42,6 +60,11 @@ func NewServerConfig(logger log.Logger, certFile, keyFile, minVersion, maxVersio
 		return nil, fmt.Errorf("TLS cipher suite name to ID conversion: %v", err)
 	}
 
+	curvePreferenceIDs, err := mapCurveNamesToIDs(curvePreferences)
+	if err != nil {
+		return nil, fmt.Errorf("TLS curve preference name to ID conversion: %v", err)
+	}
+
 	tlsClientAuthType, err := parseClientAuthType(clientAuthType)
 	if err != nil {
 		return nil, fmt.Errorf("can not parse TLS Client authentication policy: %w", err)
@@ -53,9 +76,11 @@ func NewServerConfig(logger log.Logger, certFile, keyFile, minVersion, maxVersio
 		// If CipherSuites is nil, a default list of secure cipher suites is used.
 		// Note that TLS 1.3 ciphersuites are not configurable.
 		CipherSuites: cipherSuiteIDs,
-		ClientAuth:   tlsClientAuthType,
-		MinVersion:   tlsMinVersion,
-		MaxVersion:   tlsMaxVersion,
+		// If CurvePreferences is nil, a default list of secure curves is used.
+		CurvePreferences: curvePreferenceIDs,
+		ClientAuth:       tlsClientAuthType,
+		MinVersion:       tlsMinVersion,
+		MaxVersion:       tlsMaxVersion,
 	}
 
 	return tlsCfg, nil
@@ -108,6 +133,25 @@ func mapCipherNamesToIDs(rawTLSCipherSuites []string) ([]uint16, error) {
 	return cipherSuites, nil
 }
 
+func mapCurveNamesToIDs(rawTLSCurvePreferences []string) ([]tls.CurveID, error) {
+	if rawTLSCurvePreferences == nil {
+		return nil, nil
+	}
+
+	curvePreferences := []tls.CurveID{}
+
+	for _, name := range rawTLSCurvePreferences {
+		id, ok := curveIDs[name]
+		if !ok {
+			return nil, fmt.Errorf("unknown TLSCurve: %s", name)
+		}
+
+		curvePreferences = append(curvePreferences, id)
+	}
+
+	return curvePreferences, nil
+}
+
 func parseClientAuthType(rawAuthType string) (tls.ClientAuthType, error) {
 	switch rawAuthType {
 	case "NoClientCert":

tls/config_test.go

@@ -0,0 +1,147 @@
+package tls
+
+import (
+	"crypto/tls"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/observatorium/api/logger"
+)
+
+func TestMapCurveNamesToIDs(t *testing.T) {
+	tests := []struct {
+		name       string
+		input      []string
+		want       []tls.CurveID
+		errContain string
+	}{
+		{
+			name:  "nil input",
+			input: nil,
+			want:  nil,
+		},
+		{
+			name: "all supported names (IANA and Go constant)",
+			input: []string{
+				// X25519 and the ML-KEM hybrids: IANA name == Go constant name.
+				"X25519",
+				"X25519MLKEM768",
+				"SecP256r1MLKEM768",
+				"SecP384r1MLKEM1024",
+				// Classic EC curves: IANA name and Go constant name.
+				"secp256r1", "CurveP256",
+				"secp384r1", "CurveP384",
+				"secp521r1", "CurveP521",
+			},
+			want: []tls.CurveID{
+				tls.X25519,
+				tls.X25519MLKEM768,
+				tls.SecP256r1MLKEM768,
+				tls.SecP384r1MLKEM1024,
+				tls.CurveP256, tls.CurveP256,
+				tls.CurveP384, tls.CurveP384,
+				tls.CurveP521, tls.CurveP521,
+			},
+		},
+		{
+			name:  "mixed IANA and Go constant names",
+			input: []string{"secp256r1", "CurveP384"},
+			want:  []tls.CurveID{tls.CurveP256, tls.CurveP384},
+		},
+		{
+			name:       "unknown curve name",
+			input:      []string{"CurveUnknown"},
+			errContain: "unknown TLSCurve: CurveUnknown",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got, err := mapCurveNamesToIDs(tc.input)
+			if tc.errContain != "" {
+				require.Error(t, err)
+				require.ErrorContains(t, err, tc.errContain)
+				return
+			}
+
+			require.NoError(t, err)
+			require.Equal(t, tc.want, got)
+		})
+	}
+}
+
+func TestNewServerConfigCurvePreferences(t *testing.T) {
+	certPath, keyPath, cleanCerts, err := newSelfSignedCert("localhost")
+	require.NoError(t, err)
+	defer cleanCerts()
+
+	l := logger.NewLogger("info", logger.LogFormatLogfmt, "")
+
+	tests := []struct {
+		name        string
+		curves      []string
+		want        []tls.CurveID
+		errContains []string
+	}{
+		{
+			name:   "omitted uses default curves",
+			curves: nil,
+			want:   nil,
+		},
+		{
+			name: "configured curve preferences",
+			curves: []string{
+				"X25519MLKEM768",
+				"X25519",
+				"secp256r1",
+				"CurveP384",
+				"secp521r1",
+				"SecP256r1MLKEM768",
+				"SecP384r1MLKEM1024",
+			},
+			want: []tls.CurveID{
+				tls.X25519MLKEM768,
+				tls.X25519,
+				tls.CurveP256,
+				tls.CurveP384,
+				tls.CurveP521,
+				tls.SecP256r1MLKEM768,
+				tls.SecP384r1MLKEM1024,
+			},
+		},
+		{
+			name:   "invalid curve preferences",
+			curves: []string{"CurveUnknown"},
+			errContains: []string{
+				"TLS curve preference name to ID conversion",
+				"unknown TLSCurve: CurveUnknown",
+			},
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			cfg, err := NewServerConfig(
+				l,
+				certPath,
+				keyPath,
+				"VersionTLS13",
+				"VersionTLS13",
+				"RequestClientCert",
+				nil,
+				tc.curves,
+			)
+			if len(tc.errContains) > 0 {
+				require.Error(t, err)
+				for _, msg := range tc.errContains {
+					require.ErrorContains(t, err, msg)
+				}
+				return
+			}
+
+			require.NoError(t, err)
+			require.Equal(t, tc.want, cfg.CurvePreferences)
+		})
+	}
+}