kirin: add autocert functionality

kirin.go

@@ -1,6 +1,7 @@
 package kirin
 
 import (
+	"crypto/tls"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -16,6 +17,7 @@ import (
 	"github.com/lightningnetwork/lnd/build"
 	"github.com/lightningnetwork/lnd/cert"
 	"github.com/lightningnetwork/lnd/lnrpc"
+	"golang.org/x/crypto/acme/autocert"
 	"gopkg.in/yaml.v2"
 )
 
@@ -80,19 +82,57 @@ func start() error {
 		Handler: http.HandlerFunc(servicesProxy.ServeHTTP),
 	}
 
-	// Ensure we create TLS key and certificate if they don't exist.
+	// Create TLS certificates.
 	tlsKeyFile := filepath.Join(kirinDataDir, defaultTLSKeyFilename)
 	tlsCertFile := filepath.Join(kirinDataDir, defaultTLSCertFilename)
-	if !fileExists(tlsCertFile) && !fileExists(tlsKeyFile) {
-		log.Infof("Generating TLS certificates...")
-		err := cert.GenCertPair(
-			"kirin autogenerated cert", tlsCertFile, tlsKeyFile,
-			nil, nil, cert.DefaultAutogenValidity,
-		)
-		if err != nil {
-			return err
+	switch {
+	// When using autocert, we set a TLSConfig on the server so the key and
+	// cert file we pass in are ignored and don't need to exist.
+	case cfg.AutoCert:
+		serverName := cfg.ServerName
+		if serverName == "" {
+			return fmt.Errorf("servername option is required for " +
+				"secure operation")
+		}
+
+		certDir := filepath.Join(kirinDataDir, "autocert")
+		log.Infof("Configuring autocert for server %v with cache dir "+
+			"%v", serverName, certDir)
+
+		manager := autocert.Manager{
+			Cache:      autocert.DirCache(certDir),
+			Prompt:     autocert.AcceptTOS,
+			HostPolicy: autocert.HostWhitelist(serverName),
+		}
+
+		go func() {
+			err := http.ListenAndServe(
+				":http", manager.HTTPHandler(nil),
+			)
+			if err != nil {
+				log.Errorf("autocert http: %v", err)
+			}
+		}()
+		server.TLSConfig = &tls.Config{
+			GetCertificate: manager.GetCertificate,
+		}
+
+	// If we're not using autocert, we want to create self-signed TLS certs
+	// and save them at the specified location (if they don't already
+	// exist).
+	default:
+		if !fileExists(tlsCertFile) && !fileExists(tlsKeyFile) {
+			log.Infof("Generating TLS certificates...")
+			err := cert.GenCertPair(
+				"kirin autogenerated cert", tlsCertFile,
+				tlsKeyFile, nil, nil,
+				cert.DefaultAutogenValidity,
+			)
+			if err != nil {
+				return err
+			}
+			log.Infof("Done generating TLS certificates")
 		}
-		log.Infof("Done generating TLS certificates")
 	}
 
 	// The ListenAndServeTLS below will block until shut down or an error