envoy: log mtls failures

This implements limited listener-based access logging for downstream
transport failures, only enabled when downstream_mtls.enforcement is
set to 'reject_connection'. Client certificate details and the error
message will be logged.

Additionally, the new key 'client-certificate' can be set in the
access_log_fields list in the configuration, which will add peer
certificate properties (issuer, subject, SANs) to the existing
per-request http logs.

config/envoyconfig/listeners.go

@@ -139,15 +139,10 @@ func listenerAccessLog() []*envoy_config_accesslog_v3.AccessLog {
 	}
 	tcp := marshalAny(
 		&envoy_extensions_access_loggers_grpc_v3.TcpGrpcAccessLogConfig{CommonConfig: cc})
-	http := marshalAny(
-		&envoy_extensions_access_loggers_grpc_v3.HttpGrpcAccessLogConfig{CommonConfig: cc})
 	return []*envoy_config_accesslog_v3.AccessLog{
 		{
 			Name:       "envoy.access_loggers.tcp_grpc",
 			ConfigType: &envoy_config_accesslog_v3.AccessLog_TypedConfig{TypedConfig: tcp},
-		}, {
-			Name:       "envoy.access_loggers.http_grpc",
-			ConfigType: &envoy_config_accesslog_v3.AccessLog_TypedConfig{TypedConfig: http},
 		},
 	}
 }
@@ -162,7 +157,9 @@ func (b *Builder) buildMainListener(
 		li.ListenerFilters = append(li.ListenerFilters, ProxyProtocolFilter())
 	}
 
-	li.AccessLog = listenerAccessLog() // XXX
+	if cfg.Options.DownstreamMTLS.Enforcement == config.MTLSEnforcementRejectConnection {
+		li.AccessLog = listenerAccessLog()
+	}
 
 	if cfg.Options.InsecureServer {
 		li.Address = buildAddress(cfg.Options.Addr, 80)

internal/controlplane/grpc_accesslog.go

@@ -2,13 +2,11 @@ package controlplane
 
 import (
 	"context"
-	"encoding/json"
 	"strings"
 
 	envoy_data_accesslog_v3 "github.com/envoyproxy/go-control-plane/envoy/data/accesslog/v3"
 	envoy_service_accesslog_v3 "github.com/envoyproxy/go-control-plane/envoy/service/accesslog/v3"
 	"github.com/rs/zerolog"
-	"google.golang.org/protobuf/encoding/protojson"
 
 	"github.com/pomerium/pomerium/internal/log"
 )
@@ -43,18 +41,18 @@ func accessLogListener(
 	ctx context.Context, msg *envoy_service_accesslog_v3.StreamAccessLogsMessage,
 ) {
 	for _, entry := range msg.GetTcpLogs().GetLogEntry() {
-		e, _ := protojson.Marshal(entry)
-		log.Info(ctx).
-			Str("service", "envoy").
-			Interface("log", json.RawMessage(e)).
-			Msg("listener connect (TCP log)")
-	}
-	for _, entry := range msg.GetHttpLogs().GetLogEntry() {
-		e, _ := protojson.Marshal(entry)
-		log.Info(ctx).
-			Str("service", "envoy").
-			Interface("log", json.RawMessage(e)).
-			Msg("listener connect (HTTP log)")
+		failure := entry.GetCommonProperties().GetDownstreamTransportFailureReason()
+		if failure == "" {
+			continue
+		}
+		e := log.Info(ctx).Str("service", "envoy")
+		dict := zerolog.Dict()
+		populateCertEventDict(entry.GetCommonProperties().GetTlsProperties().GetPeerCertificateProperties(), dict)
+		e.Dict("client-certificate", dict)
+		e.Str("ip", entry.GetCommonProperties().GetDownstreamRemoteAddress().GetSocketAddress().GetAddress())
+		e.Str("tls-sni-hostname", entry.GetCommonProperties().GetTlsProperties().GetTlsSniHostname())
+		e.Str("downstream-transport-failure-reason", failure)
+		e.Msg("listener connection failure")
 	}
 }
 
@@ -121,7 +119,34 @@ func populateLogEvent(
 		return evt.Str(string(field), entry.GetCommonProperties().GetUpstreamCluster())
 	case log.AccessLogFieldUserAgent:
 		return evt.Str(string(field), entry.GetRequest().GetUserAgent())
+	case log.AccessLogFieldClientCertificate:
+		dict := zerolog.Dict()
+		populateCertEventDict(entry.GetCommonProperties().GetTlsProperties().GetPeerCertificateProperties(), dict)
+		return evt.Dict(string(field), dict)
 	default:
 		return evt
 	}
 }
+
+func populateCertEventDict(cert *envoy_data_accesslog_v3.TLSProperties_CertificateProperties, dict *zerolog.Event) {
+	if cert.Issuer != "" {
+		dict.Str("issuer", cert.Issuer)
+	}
+	if cert.Subject != "" {
+		dict.Str("subject", cert.Subject)
+	}
+	if len(cert.SubjectAltName) > 0 {
+		arr := zerolog.Arr()
+		for _, san := range cert.SubjectAltName {
+			// follow openssl GENERAL_NAME_print formatting
+			// envoy only provides dns and uri SANs at the moment
+			switch san := san.GetSan().(type) {
+			case *envoy_data_accesslog_v3.TLSProperties_CertificateProperties_SubjectAltName_Dns:
+				arr.Str("DNS:" + san.Dns)
+			case *envoy_data_accesslog_v3.TLSProperties_CertificateProperties_SubjectAltName_Uri:
+				arr.Str("URI:" + san.Uri)
+			}
+		}
+		dict.Array("subjectAltName", arr)
+	}
+}

internal/log/access.go

@@ -24,6 +24,7 @@ const (
 	AccessLogFieldSize                AccessLogField = "size"
 	AccessLogFieldUpstreamCluster     AccessLogField = "upstream-cluster"
 	AccessLogFieldUserAgent           AccessLogField = "user-agent"
+	AccessLogFieldClientCertificate   AccessLogField = "client-certificate"
 )
 
 var defaultAccessLogFields = []AccessLogField{
@@ -64,6 +65,7 @@ var accessLogFieldLookup = map[AccessLogField]struct{}{
 	AccessLogFieldSize:                {},
 	AccessLogFieldUpstreamCluster:     {},
 	AccessLogFieldUserAgent:           {},
+	AccessLogFieldClientCertificate:   {},
 }
 
 // Validate returns an error if the access log field is invalid.