letsencrypt: Fixed renewals

By chaining in a middleware handler and using newly exposed hooks from the acme package, we're able to proxy ACME requests on port 443 to the ACME client listening on a different port.

caddy/letsencrypt/handler.go

+package letsencrypt
+
+import (
+	"crypto/tls"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+	"sync"
+	"sync/atomic"
+
+	"github.com/mholt/caddy/middleware"
+)
+
+// Handler is a Caddy middleware that can proxy ACME requests
+// to the real ACME endpoint. This is necessary to renew certificates
+// while the server is running. Obviously, a site served on port
+// 443 (HTTPS) binds to that port, so another listener created by
+// our acme client can't bind successfully and solve the challenge.
+// Thus, we chain this handler in so that it can, when activated,
+// proxy ACME requests to an ACME client listening on an alternate
+// port.
+type Handler struct {
+	sync.Mutex      // protects the ChallengePath property
+	Next            middleware.Handler
+	ChallengeActive int32  // use sync/atomic for speed to set/get this flag
+	ChallengePath   string // the exact request path to match before proxying
+}
+
+// ServeHTTP is basically a no-op unless an ACME challenge is active on this host
+// and the request path matches the expected path exactly.
+func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
+	// Only if challenge is active
+	if atomic.LoadInt32(&h.ChallengeActive) == 1 {
+		h.Lock()
+		path := h.ChallengePath
+		h.Unlock()
+
+		// Request path must be correct; if so, proxy to ACME client
+		if r.URL.Path == path {
+			upstream, err := url.Parse("https://" + r.Host + ":" + alternatePort)
+			if err != nil {
+				return http.StatusInternalServerError, err
+			}
+			proxy := httputil.NewSingleHostReverseProxy(upstream)
+			proxy.Transport = &http.Transport{
+				TLSClientConfig: &tls.Config{InsecureSkipVerify: true}, // client uses self-signed cert
+			}
+			proxy.ServeHTTP(w, r)
+			return 0, nil
+		}
+	}
+
+	return h.Next.ServeHTTP(w, r)
+}
+
+// ChallengeOn enables h to proxy ACME requests.
+func (h *Handler) ChallengeOn(challengePath string) {
+	h.Lock()
+	h.ChallengePath = challengePath
+	h.Unlock()
+	atomic.StoreInt32(&h.ChallengeActive, 1)
+}
+
+// ChallengeOff disables ACME proxying from this h.
+func (h *Handler) ChallengeOff(success bool) {
+	atomic.StoreInt32(&h.ChallengeActive, 0)
+}

caddy/letsencrypt/letsencrypt.go

@@ -82,7 +82,7 @@ func Activate(configs []server.Config) ([]server.Config, error) {
 			return configs, errors.New("error creating client: " + err.Error())
 		}
 
-		// client is ready, so let's get free, trusted SSL certificates! yeah!
+		// client is ready, so let's get free, trusted SSL certificates!
 	Obtain:
 		certificates, failures := obtainCertificates(client, serverConfigs)
 		if len(failures) > 0 {
@@ -128,7 +128,7 @@ func Activate(configs []server.Config) ([]server.Config, error) {
 	}
 
 	// renew all certificates that need renewal
-	renewCertificates(configs)
+	renewCertificates(configs, false)
 
 	// keep certificates renewed and OCSP stapling updated
 	go maintainAssets(configs, stopChan)
@@ -167,8 +167,8 @@ func configQualifies(cfg server.Config, allConfigs []server.Config) bool {
 		cfg.Host != "" &&
 		cfg.Host != "0.0.0.0" &&
 		cfg.Host != "::1" &&
-		!strings.HasPrefix(cfg.Host, "127.") &&
-		// TODO: Also exclude 10.* and 192.168.* addresses?
+		!strings.HasPrefix(cfg.Host, "127.") && // to use a boulder on your own machine, add fake domain to hosts file
+		// not excluding 10.* and 192.168.* hosts for possibility of running internal Boulder instance
 
 		// make sure an HTTPS version of this config doesn't exist in the list already
 		!hostHasOtherScheme(cfg.Host, "https", allConfigs)
@@ -215,6 +215,14 @@ func existingCertAndKey(host string) bool {
 // disk (if already exists) or created new and registered via ACME
 // and saved to the file system for next time.
 func newClient(leEmail string) (*acme.Client, error) {
+	return newClientPort(leEmail, exposePort)
+}
+
+// newClientPort does the same thing as newClient, except it creates a
+// new client with a custom port used for ACME transactions instead of
+// the default port. This is important if the default port is already in
+// use or is not exposed to the public, etc.
+func newClientPort(leEmail, port string) (*acme.Client, error) {
 	// Look up or create the LE user account
 	leUser, err := getUser(leEmail)
 	if err != nil {
@@ -222,7 +230,7 @@ func newClient(leEmail string) (*acme.Client, error) {
 	}
 
 	// The client facilitates our communication with the CA server.
-	client, err := acme.NewClient(CAUrl, &leUser, rsaKeySizeToUse, exposePort)
+	client, err := acme.NewClient(CAUrl, &leUser, rsaKeySizeToUse, port)
 	if err != nil {
 		return nil, err
 	}
@@ -325,6 +333,17 @@ func autoConfigure(cfg *server.Config, allConfigs []server.Config) []server.Conf
 		cfg.Port = "https"
 	}
 
+	// Chain in ACME middleware proxy if we use up the SSL port
+	if cfg.Port == "https" || cfg.Port == "443" {
+		handler := new(Handler)
+		mid := func(next middleware.Handler) middleware.Handler {
+			handler.Next = next
+			return handler
+		}
+		cfg.Middleware["/"] = append(cfg.Middleware["/"], mid)
+		acmeHandlers[cfg.Host] = handler
+	}
+
 	// Set up http->https redirect as long as there isn't already
 	// a http counterpart in the configs
 	if !hostHasOtherScheme(cfg.Host, "http", allConfigs) {
@@ -440,6 +459,11 @@ const (
 	// then port 443 must be forwarded to exposePort.
 	exposePort = "443"
 
+	// If port 443 is in use by a Caddy server instance, then this is
+	// port on which the acme client will solve challenges. (Whatever is
+	// listening on port 443 must proxy ACME requests to this port.)
+	alternatePort = "5033"
+
 	// How often to check certificates for renewal.
 	renewInterval = 24 * time.Hour
 

caddy/letsencrypt/maintain.go

@@ -33,15 +33,17 @@ func maintainAssets(configs []server.Config, stopChan chan struct{}) {
 	for {
 		select {
 		case <-renewalTicker.C:
-			if n, errs := renewCertificates(configs); len(errs) > 0 {
+			n, errs := renewCertificates(configs, true)
+			if len(errs) > 0 {
 				for _, err := range errs {
 					log.Printf("[ERROR] cert renewal: %v\n", err)
 				}
-				if n > 0 && OnChange != nil {
-					err := OnChange()
-					if err != nil {
-						log.Printf("[ERROR] onchange after cert renewal: %v\n", err)
-					}
+			}
+			// even if there was an error, some renewals may have succeeded
+			if n > 0 && OnChange != nil {
+				err := OnChange()
+				if err != nil {
+					log.Printf("[ERROR] onchange after cert renewal: %v\n", err)
 				}
 			}
 		case <-ocspTicker.C:
@@ -69,11 +71,20 @@ func maintainAssets(configs []server.Config, stopChan chan struct{}) {
 // through this function; all changes happen directly on disk.
 // It returns the number of certificates renewed and any errors
 // that occurred. It only performs a renewal if necessary.
-func renewCertificates(configs []server.Config) (int, []error) {
+// If useCustomPort is true, a custom port will be used, and
+// whatever is listening at 443 better proxy ACME requests to it.
+// Otherwise, the acme package will create its own listener on 443.
+func renewCertificates(configs []server.Config, useCustomPort bool) (int, []error) {
 	log.Print("[INFO] Processing certificate renewals...")
 	var errs []error
 	var n int
 
+	defer func() {
+		// reset these so as to not interfere with other challenges
+		acme.OnSimpleHTTPStart = nil
+		acme.OnSimpleHTTPEnd = nil
+	}()
+
 	for _, cfg := range configs {
 		// Host must be TLS-enabled and have existing assets managed by LE
 		if !cfg.TLS.Enabled || !existingCertAndKey(cfg.Host) {
@@ -100,7 +111,12 @@ func renewCertificates(configs []server.Config) (int, []error) {
 		// Renew with two weeks or less remaining.
 		if daysLeft <= 14 {
 			log.Printf("[INFO] There are %d days left on the certificate of %s. Trying to renew now.", daysLeft, cfg.Host)
-			client, err := newClient("") // email not used for renewal
+			var client *acme.Client
+			if useCustomPort {
+				client, err = newClientPort("", alternatePort) // email not used for renewal
+			} else {
+				client, err = newClient("")
+			}
 			if err != nil {
 				errs = append(errs, err)
 				continue
@@ -124,6 +140,10 @@ func renewCertificates(configs []server.Config) (int, []error) {
 			certMeta.Certificate = certBytes
 			certMeta.PrivateKey = privBytes
 
+			// Tell the handler to accept and proxy acme request in order to solve challenge
+			acme.OnSimpleHTTPStart = acmeHandlers[cfg.Host].ChallengeOn
+			acme.OnSimpleHTTPEnd = acmeHandlers[cfg.Host].ChallengeOff
+
 			// Renew certificate.
 			// TODO: revokeOld should be an option in the caddyfile
 			// TODO: bundle should be an option in the caddyfile as well :)
@@ -148,11 +168,16 @@ func renewCertificates(configs []server.Config) (int, []error) {
 
 			saveCertsAndKeys([]acme.CertificateResource{newCertMeta})
 			n++
-		} else if daysLeft <= 14 {
-			// Warn on 14 days remaining
-			log.Printf("[WARN] There are %d days left on the certificate for %s. Will renew when 7 days remain.\n", daysLeft, cfg.Host)
+		} else if daysLeft <= 30 {
+			// Warn on 30 days remaining. TODO: Just do this once...
+			log.Printf("[WARN] There are %d days left on the certificate for %s. Will renew when 14 days remain.\n", daysLeft, cfg.Host)
 		}
 	}
 
 	return n, errs
 }
+
+// acmeHandlers is a map of host to ACME handler. These
+// are used to proxy ACME requests to the ACME client
+// when port 443 is in use.
+var acmeHandlers = make(map[string]*Handler)