Update TLS certificates, generate certificate if not found.

We now notice that a TLS certificate on disk has changed, and we
generate a self-signed certificate if none is found.

README

@@ -4,15 +4,11 @@
 
     CGO_ENABLED=0 go build -ldflags='-s -w'
 
-## Create a server certificate
-
-    mkdir data
-    openssl req -newkey rsa:2048 -nodes -keyout data/key.pem -x509 -days 365 -out data/cert.pem
-
 ## Set the server administrator credentials
 
 This step is optional.
 
+    mkdir data
     echo 'god:topsecret' > data/passwd
 
 ## Set up a group
@@ -110,6 +106,16 @@ For a 32-bit MIPS board with no hardware floating point (WNDR3800, etc.):
 Set up a user *galene* on your server, then do:
 
     rsync -a galene static data groups galene@server.example.org:
+
+If you don't have a TLS certificate, Galène will generate a self-signed
+certificate automatically (and print a warning to the logs).  If you have
+a certificate, install it in the files `data/cert.pem` and `data/key.pem`:
+
+   ssh galene@server.example.org
+   sudo cp /etc/letsencrypt/live/server.example.org/fullchain.pem data/cert.pem
+   sudo cp /etc/letsencrypt/live/server.example.org/key.pem data/key.pem
+   sudo chown galene:galene data/*.pem
+   sudo chmod go-rw data/key.pem
 
 Now run the binary on the server:
 

webserver/certificate.go

@@ -0,0 +1,98 @@
+package webserver
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/tls"
+	"crypto/x509"
+	"log"
+	"math/big"
+	"os"
+	"path/filepath"
+	"sync/atomic"
+	"time"
+)
+
+type certInfo struct {
+	certificate *tls.Certificate
+	keyTime     time.Time
+	certTime    time.Time
+}
+
+var certificate atomic.Value
+
+func generateCertificate(dataDir string) (tls.Certificate, error) {
+	priv, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		return tls.Certificate{}, err
+	}
+
+	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
+	serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
+	now := time.Now()
+
+	template := x509.Certificate{
+		SerialNumber:          serialNumber,
+		NotBefore:             now,
+		NotAfter:              now.Add(365 * 24 * time.Hour),
+		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
+		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
+		BasicConstraintsValid: true,
+	}
+	bytes, err := x509.CreateCertificate(
+		rand.Reader, &template, &template, &priv.PublicKey, priv,
+	)
+	if err != nil {
+		return tls.Certificate{}, err
+	}
+
+	return tls.Certificate{
+		Certificate: [][]byte{bytes},
+		PrivateKey:  priv,
+	}, nil
+}
+
+func fileTime(filename string) time.Time {
+	fi, err := os.Stat(filename)
+	if err != nil {
+		if !os.IsNotExist(err) {
+			log.Printf("%v: %v", filename, err)
+		}
+		return time.Time{}
+	}
+	return fi.ModTime()
+}
+
+func getCertificate(dataDir string) (*tls.Certificate, error) {
+	info, ok := certificate.Load().(*certInfo)
+
+	certFile := filepath.Join(dataDir, "cert.pem")
+	keyFile := filepath.Join(dataDir, "key.pem")
+	certTime := fileTime(certFile)
+	keyTime := fileTime(keyFile)
+
+	if !ok || !info.certTime.Equal(certTime) || !info.keyTime.Equal(keyTime) {
+		var cert tls.Certificate
+		if certTime.Equal(time.Time{}) || keyTime.Equal(time.Time{}) {
+			log.Printf("Generating self-signed certificate")
+			var err error
+			cert, err = generateCertificate(dataDir)
+			if err != nil {
+				return nil, err
+			}
+		} else {
+			var err error
+			cert, err = tls.LoadX509KeyPair(certFile, keyFile)
+			if err != nil {
+				return nil, err
+			}
+		}
+		info = &certInfo{
+			certificate: &cert,
+			certTime:    certTime,
+			keyTime:     keyTime,
+		}
+		certificate.Store(info)
+	}
+	return info.certificate, nil
+}

webserver/webserver.go

@@ -3,6 +3,7 @@ package webserver
 import (
 	"bufio"
 	"context"
+	"crypto/tls"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -55,6 +56,13 @@ func Serve(address string, dataDir string) error {
 		ReadHeaderTimeout: 60 * time.Second,
 		IdleTimeout:       120 * time.Second,
 	}
+	if !Insecure {
+		s.TLSConfig = &tls.Config{
+			GetCertificate: func(hello *tls.ClientHelloInfo) (*tls.Certificate, error) {
+				return getCertificate(dataDir)
+			},
+		}
+	}
 	s.RegisterOnShutdown(func() {
 		group.Range(func(g *group.Group) bool {
 			go g.Shutdown("server is shutting down")
@@ -67,10 +75,7 @@ func Serve(address string, dataDir string) error {
 	var err error
 
 	if !Insecure {
-		err = s.ListenAndServeTLS(
-			filepath.Join(dataDir, "cert.pem"),
-			filepath.Join(dataDir, "key.pem"),
-		)
+		err = s.ListenAndServeTLS("", "")
 	} else {
 		err = s.ListenAndServe()
 	}
@@ -273,8 +278,8 @@ func groupHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if r.URL.Path != "/group/" + name {
-		http.Redirect(w, r, "/group/" + name,
+	if r.URL.Path != "/group/"+name {
+		http.Redirect(w, r, "/group/"+name,
 			http.StatusPermanentRedirect)
 		return
 	}
@@ -433,7 +438,7 @@ func statsHandler(w http.ResponseWriter, r *http.Request, dataDir string) {
 	fmt.Fprintf(w, "</body></html>\n")
 }
 
-var wsUpgrader = websocket.Upgrader {
+var wsUpgrader = websocket.Upgrader{
 	HandshakeTimeout: 30 * time.Second,
 }