TLS certs reloader (dexidp#2964)

Signed-off-by: Sean Liao <sean+git@liao.dev>
FlockFreight · Oct 4, 2023 · 3256ffd · 3256ffd
1 parent c9c020c
commit 3256ffd
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Showing 3 changed files with 140 additions and 29 deletions.
diff --git a/cmd/dex/serve.go b/cmd/dex/serve.go
@@ -10,14 +10,18 @@ import (
 	"net/http"
 	"net/http/pprof"
 	"os"
+	"os/signal"
+	"path/filepath"
 	"runtime"
 	"strings"
+	"sync/atomic"
 	"syscall"
 	"time"
 
 	gosundheit "github.com/AppsFlyer/go-sundheit"
 	"github.com/AppsFlyer/go-sundheit/checks"
 	gosundheithttp "github.com/AppsFlyer/go-sundheit/http"
+	"github.com/fsnotify/fsnotify"
 	"github.com/ghodss/yaml"
 	grpcprometheus "github.com/grpc-ecosystem/go-grpc-prometheus"
 	"github.com/oklog/run"
@@ -142,41 +146,26 @@ func runServe(options serveOptions) error {
 	}
 
 	if c.GRPC.TLSCert != "" {
-		// Parse certificates from certificate file and key file for server.
-		cert, err := tls.LoadX509KeyPair(c.GRPC.TLSCert, c.GRPC.TLSKey)
-		if err != nil {
-			return fmt.Errorf("invalid config: error parsing gRPC certificate file: %v", err)
-		}
-
-		tlsConfig := tls.Config{
-			Certificates:             []tls.Certificate{cert},
+		baseTLSConfig := &tls.Config{
 			MinVersion:               tls.VersionTLS12,
 			CipherSuites:             allowedTLSCiphers,
 			PreferServerCipherSuites: true,
 		}
 
-		if c.GRPC.TLSClientCA != "" {
-			// Parse certificates from client CA file to a new CertPool.
-			cPool := x509.NewCertPool()
-			clientCert, err := os.ReadFile(c.GRPC.TLSClientCA)
-			if err != nil {
-				return fmt.Errorf("invalid config: reading from client CA file: %v", err)
-			}
-			if !cPool.AppendCertsFromPEM(clientCert) {
-				return errors.New("invalid config: failed to parse client CA")
-			}
-
-			tlsConfig.ClientAuth = tls.RequireAndVerifyClientCert
-			tlsConfig.ClientCAs = cPool
+		tlsConfig, err := newTLSReloader(logger, c.GRPC.TLSCert, c.GRPC.TLSKey, c.GRPC.TLSClientCA, baseTLSConfig)
+		if err != nil {
+			return fmt.Errorf("invalid config: get gRPC TLS: %v", err)
+		}
 
+		if c.GRPC.TLSClientCA != "" {
 			// Only add metrics if client auth is enabled
 			grpcOptions = append(grpcOptions,
 				grpc.StreamInterceptor(grpcMetrics.StreamServerInterceptor()),
 				grpc.UnaryInterceptor(grpcMetrics.UnaryServerInterceptor()),
 			)
 		}
 
-		grpcOptions = append(grpcOptions, grpc.Creds(credentials.NewTLS(&tlsConfig)))
+		grpcOptions = append(grpcOptions, grpc.Creds(credentials.NewTLS(tlsConfig)))
 	}
 
 	s, err := c.Storage.Config.Open(logger)
@@ -431,18 +420,25 @@ func runServe(options serveOptions) error {
 			return fmt.Errorf("listening (%s) on %s: %v", name, c.Web.HTTPS, err)
 		}
 
+		baseTLSConfig := &tls.Config{
+			MinVersion:               tls.VersionTLS12,
+			CipherSuites:             allowedTLSCiphers,
+			PreferServerCipherSuites: true,
+		}
+
+		tlsConfig, err := newTLSReloader(logger, c.Web.TLSCert, c.Web.TLSKey, "", baseTLSConfig)
+		if err != nil {
+			return fmt.Errorf("invalid config: get HTTP TLS: %v", err)
+		}
+
 		server := &http.Server{
-			Handler: serv,
-			TLSConfig: &tls.Config{
-				CipherSuites:             allowedTLSCiphers,
-				PreferServerCipherSuites: true,
-				MinVersion:               tls.VersionTLS12,
-			},
+			Handler:   serv,
+			TLSConfig: tlsConfig,
 		}
 		defer server.Close()
 
 		group.Add(func() error {
-			return server.ServeTLS(l, c.Web.TLSCert, c.Web.TLSKey)
+			return server.ServeTLS(l, "", "")
 		}, func(err error) {
 			ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
 			defer cancel()
@@ -563,3 +559,114 @@ func pprofHandler(router *http.ServeMux) {
 	router.HandleFunc("/debug/pprof/symbol", pprof.Symbol)
 	router.HandleFunc("/debug/pprof/trace", pprof.Trace)
 }
+
+// newTLSReloader returns a [tls.Config] with GetCertificate or GetConfigForClient set
+// to reload certificates from the given paths on SIGHUP or on file creates (atomic update via rename).
+func newTLSReloader(logger log.Logger, certFile, keyFile, caFile string, baseConfig *tls.Config) (*tls.Config, error) {
+	// trigger reload on channel
+	sigc := make(chan os.Signal, 1)
+	signal.Notify(sigc, syscall.SIGHUP)
+
+	// files to watch
+	watchFiles := map[string]struct{}{
+		certFile: {},
+		keyFile:  {},
+	}
+	if caFile != "" {
+		watchFiles[caFile] = struct{}{}
+	}
+	watchDirs := make(map[string]struct{}) // dedupe dirs
+	for f := range watchFiles {
+		dir := filepath.Dir(f)
+		if !strings.HasPrefix(f, dir) {
+			// normalize name to have ./ prefix if only a local path was provided
+			// can't pass "" to watcher.Add
+			watchFiles[dir+string(filepath.Separator)+f] = struct{}{}
+		}
+		watchDirs[dir] = struct{}{}
+	}
+	// trigger reload on file change
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		return nil, fmt.Errorf("create watcher for TLS reloader: %v", err)
+	}
+	// recommended by fsnotify: watch the dir to handle renames
+	// https://pkg.go.dev/github.com/fsnotify/fsnotify#hdr-Watching_files
+	for dir := range watchDirs {
+		logger.Debugf("watching dir: %v", dir)
+		err := watcher.Add(dir)
+		if err != nil {
+			return nil, fmt.Errorf("watch dir for TLS reloader: %v", err)
+		}
+	}
+
+	// load once outside the goroutine so we can return an error on misconfig
+	initialConfig, err := loadTLSConfig(certFile, keyFile, caFile, baseConfig)
+	if err != nil {
+		return nil, fmt.Errorf("load TLS config: %v", err)
+	}
+
+	// stored version of current tls config
+	ptr := &atomic.Pointer[tls.Config]{}
+	ptr.Store(initialConfig)
+
+	// start background worker to reload certs
+	go func() {
+	loop:
+		for {
+			select {
+			case sig := <-sigc:
+				logger.Debug("reloading cert from signal: %v", sig)
+			case evt := <-watcher.Events:
+				if _, ok := watchFiles[evt.Name]; !ok || !evt.Has(fsnotify.Create) {
+					continue loop
+				}
+				logger.Debug("reloading cert from fsnotify: %v %v", evt.Name, evt.Op.String())
+			case err := <-watcher.Errors:
+				logger.Errorf("TLS reloader watch: %v", err)
+			}
+
+			loaded, err := loadTLSConfig(certFile, keyFile, caFile, baseConfig)
+			if err != nil {
+				logger.Errorf("reload TLS config: %v", err)
+			}
+			ptr.Store(loaded)
+		}
+	}()
+
+	conf := &tls.Config{}
+	// https://pkg.go.dev/crypto/tls#baseConfig
+	// Server configurations must set one of Certificates, GetCertificate or GetConfigForClient.
+	if caFile != "" {
+		// grpc will use this via tls.Server for mTLS
+		conf.GetConfigForClient = func(chi *tls.ClientHelloInfo) (*tls.Config, error) { return ptr.Load(), nil }
+	} else {
+		// net/http only uses Certificates or GetCertificate
+		conf.GetCertificate = func(chi *tls.ClientHelloInfo) (*tls.Certificate, error) { return &ptr.Load().Certificates[0], nil }
+	}
+	return conf, nil
+}
+
+// loadTLSConfig loads the given file paths into a [tls.Config]
+func loadTLSConfig(certFile, keyFile, caFile string, baseConfig *tls.Config) (*tls.Config, error) {
+	cert, err := tls.LoadX509KeyPair(certFile, keyFile)
+	if err != nil {
+		return nil, fmt.Errorf("loading TLS keypair: %v", err)
+	}
+	loadedConfig := baseConfig.Clone() // copy
+	loadedConfig.Certificates = []tls.Certificate{cert}
+	if caFile != "" {
+		cPool := x509.NewCertPool()
+		clientCert, err := os.ReadFile(caFile)
+		if err != nil {
+			return nil, fmt.Errorf("reading from client CA file: %v", err)
+		}
+		if !cPool.AppendCertsFromPEM(clientCert) {
+			return nil, errors.New("failed to parse client CA")
+		}
+
+		loadedConfig.ClientAuth = tls.RequireAndVerifyClientCert
+		loadedConfig.ClientCAs = cPool
+	}
+	return loadedConfig, nil
+}
diff --git a/go.mod b/go.mod
@@ -11,6 +11,7 @@ require (
 	github.com/coreos/go-oidc/v3 v3.6.0
 	github.com/dexidp/dex/api/v2 v2.1.0
 	github.com/felixge/httpsnoop v1.0.3
+	github.com/fsnotify/fsnotify v1.6.0
 	github.com/ghodss/yaml v1.0.0
 	github.com/go-ldap/ldap/v3 v3.4.4
 	github.com/go-sql-driver/mysql v1.7.1

diff --git a/go.sum b/go.sum
@@ -65,6 +65,8 @@ github.com/felixge/httpsnoop v1.0.3 h1:s/nj+GCswXYzN5v2DpNMuMQYe+0DDwt5WVCU6CWBd
 github.com/felixge/httpsnoop v1.0.3/go.mod h1:m8KPJKqk1gH5J9DgRY2ASl2lWCfGKXixSwevea8zH2U=
 github.com/fortytw2/leaktest v1.3.0 h1:u8491cBMTQ8ft8aeV+adlcytMZylmA5nnwwkRZjI8vw=
 github.com/fortytw2/leaktest v1.3.0/go.mod h1:jDsjWgpAGjm2CA7WthBh/CdZYEPF31XHquHwclZch5g=
+github.com/fsnotify/fsnotify v1.6.0 h1:n+5WquG0fcWoWp6xPWfHdbskMCQaFnG6PfBrh1Ky4HY=
+github.com/fsnotify/fsnotify v1.6.0/go.mod h1:sl3t1tCWJFWoRz9R8WJCbQihKKwmorjAbSClcnxKAGw=
 github.com/ghodss/yaml v1.0.0 h1:wQHKEahhL6wmXdzwWG11gIVCkOv05bNOh+Rxn0yngAk=
 github.com/ghodss/yaml v1.0.0/go.mod h1:4dBDuWmgqj2HViK6kFavaiC9ZROes6MMH2rRYeMEF04=
 github.com/go-asn1-ber/asn1-ber v1.5.4 h1:vXT6d/FNDiELJnLb6hGNa309LMsrCoYFvpwHDF0+Y1A=
@@ -303,6 +305,7 @@ golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBc
 golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220908164124-27713097b956/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.2.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.8.0 h1:EBmGv8NaZBZTWvrbjNoL6HVt+IVy3QDQpJs7VRIw3tU=
 golang.org/x/sys v0.8.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=